diff --git a/.changeset/mighty-stingrays-press.md b/.changeset/mighty-stingrays-press.md
deleted file mode 100644
index 12c353dcd928..000000000000
--- a/.changeset/mighty-stingrays-press.md
+++ /dev/null
@@ -1,63 +0,0 @@
----
-'astro': patch
----
-
-Adds support for Zod discriminated unions on Action form inputs. This allows forms with different inputs to be submitted to the same action, using a given input to decide which object should be used for validation.
-
-This example accepts either a `create` or `update` form submission, and uses the `type` field to determine which object to validate against.
-
-```ts
-import { defineAction } from 'astro:actions';
-import { z } from 'astro:schema';
-
-export const server = {
-  changeUser: defineAction({
-    accept: 'form',
-    input: z.discriminatedUnion('type', [
-      z.object({
-        type: z.literal('create'),
-        name: z.string(),
-        email: z.string().email(),
-      }),
-      z.object({
-        type: z.literal('update'),
-        id: z.number(),
-        name: z.string(),
-        email: z.string().email(),
-      }),
-    ]),
-    async handler(input) {
-      if (input.type === 'create') {
-        // input is { type: 'create', name: string, email: string }
-      } else {
-        // input is { type: 'update', id: number, name: string, email: string }
-      }
-    },
-  }),
-}
-```
-
-The corresponding `create` and `update` forms may look like this:
-
-```astro
----
-import { actions } from 'astro:actions';
----
-
-<!--Create-->
-<form action={actions.changeUser} method="POST">
-  <input type="hidden" name="type" value="create" />
-  <input type="text" name="name" required />
-  <input type="email" name="email" required />
-  <button type="submit">Create User</button>
-</form>
-
-<!--Update-->
-<form action={actions.changeUser} method="POST">
-  <input type="hidden" name="type" value="update" />
-  <input type="hidden" name="id" value="user-123" />
-  <input type="text" name="name" required />
-  <input type="email" name="email" required />
-  <button type="submit">Update User</button>
-</form>
-```
diff --git a/examples/basics/package.json b/examples/basics/package.json
index a6bbf72554da..20320658e4f7 100644
--- a/examples/basics/package.json
+++ b/examples/basics/package.json
@@ -11,6 +11,6 @@
     "astro": "astro"
   },
   "dependencies": {
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/blog/package.json b/examples/blog/package.json
index 2935f2ceed86..c8bebd190646 100644
--- a/examples/blog/package.json
+++ b/examples/blog/package.json
@@ -11,9 +11,9 @@
     "astro": "astro"
   },
   "dependencies": {
-    "@astrojs/mdx": "^3.1.5",
+    "@astrojs/mdx": "^3.1.6",
     "@astrojs/rss": "^4.0.7",
     "@astrojs/sitemap": "^3.1.6",
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/component/package.json b/examples/component/package.json
index 3f44cb9385fe..1ca79c5fb1b6 100644
--- a/examples/component/package.json
+++ b/examples/component/package.json
@@ -15,7 +15,7 @@
   ],
   "scripts": {},
   "devDependencies": {
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   },
   "peerDependencies": {
     "astro": "^4.0.0"
diff --git a/examples/container-with-vitest/package.json b/examples/container-with-vitest/package.json
index 6d5aea4c37fc..45ca685d4a8b 100644
--- a/examples/container-with-vitest/package.json
+++ b/examples/container-with-vitest/package.json
@@ -12,7 +12,7 @@
     "test": "vitest run"
   },
   "dependencies": {
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "@astrojs/react": "^3.6.2",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
diff --git a/examples/framework-alpine/package.json b/examples/framework-alpine/package.json
index 1d0b64c2c346..a08659d18e6b 100644
--- a/examples/framework-alpine/package.json
+++ b/examples/framework-alpine/package.json
@@ -14,6 +14,6 @@
     "@astrojs/alpinejs": "^0.4.0",
     "@types/alpinejs": "^3.13.10",
     "alpinejs": "^3.14.1",
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/framework-lit/package.json b/examples/framework-lit/package.json
index 1aba743b6d54..2c2a88d0935c 100644
--- a/examples/framework-lit/package.json
+++ b/examples/framework-lit/package.json
@@ -13,7 +13,7 @@
   "dependencies": {
     "@astrojs/lit": "^4.3.0",
     "@webcomponents/template-shadowroot": "^0.2.1",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "lit": "^3.2.0"
   }
 }
diff --git a/examples/framework-multiple/package.json b/examples/framework-multiple/package.json
index f459c4aeff2b..c99a3ba72e2f 100644
--- a/examples/framework-multiple/package.json
+++ b/examples/framework-multiple/package.json
@@ -18,7 +18,7 @@
     "@astrojs/vue": "^4.5.0",
     "@types/react": "^18.3.5",
     "@types/react-dom": "^18.3.0",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "preact": "^10.23.2",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
diff --git a/examples/framework-preact/package.json b/examples/framework-preact/package.json
index 2d2924649b4d..222c29ccfb25 100644
--- a/examples/framework-preact/package.json
+++ b/examples/framework-preact/package.json
@@ -13,7 +13,7 @@
   "dependencies": {
     "@astrojs/preact": "^3.5.3",
     "@preact/signals": "^1.3.0",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "preact": "^10.23.2"
   }
 }
diff --git a/examples/framework-react/package.json b/examples/framework-react/package.json
index 97cb985ef9cc..ac96d6c9da74 100644
--- a/examples/framework-react/package.json
+++ b/examples/framework-react/package.json
@@ -14,7 +14,7 @@
     "@astrojs/react": "^3.6.2",
     "@types/react": "^18.3.5",
     "@types/react-dom": "^18.3.0",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "react": "^18.3.1",
     "react-dom": "^18.3.1"
   }
diff --git a/examples/framework-solid/package.json b/examples/framework-solid/package.json
index 8ccd47f5294f..351cd4d30225 100644
--- a/examples/framework-solid/package.json
+++ b/examples/framework-solid/package.json
@@ -12,7 +12,7 @@
   },
   "dependencies": {
     "@astrojs/solid-js": "^4.4.1",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "solid-js": "^1.8.22"
   }
 }
diff --git a/examples/framework-svelte/package.json b/examples/framework-svelte/package.json
index eb29897a7c45..1b983c3a1f05 100644
--- a/examples/framework-svelte/package.json
+++ b/examples/framework-svelte/package.json
@@ -12,7 +12,7 @@
   },
   "dependencies": {
     "@astrojs/svelte": "^5.7.0",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "svelte": "^4.2.19"
   }
 }
diff --git a/examples/framework-vue/package.json b/examples/framework-vue/package.json
index 004b6ebac2a5..7300890f9c83 100644
--- a/examples/framework-vue/package.json
+++ b/examples/framework-vue/package.json
@@ -12,7 +12,7 @@
   },
   "dependencies": {
     "@astrojs/vue": "^4.5.0",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "vue": "^3.5.3"
   }
 }
diff --git a/examples/hackernews/package.json b/examples/hackernews/package.json
index 4115eb8014a7..932de940d9ea 100644
--- a/examples/hackernews/package.json
+++ b/examples/hackernews/package.json
@@ -12,6 +12,6 @@
   },
   "dependencies": {
     "@astrojs/node": "^8.3.3",
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/integration/package.json b/examples/integration/package.json
index 3377faa51ecf..57f58177241e 100644
--- a/examples/integration/package.json
+++ b/examples/integration/package.json
@@ -15,7 +15,7 @@
   ],
   "scripts": {},
   "devDependencies": {
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   },
   "peerDependencies": {
     "astro": "^4.0.0"
diff --git a/examples/middleware/package.json b/examples/middleware/package.json
index a35011515d9d..d3abf03155e5 100644
--- a/examples/middleware/package.json
+++ b/examples/middleware/package.json
@@ -13,7 +13,7 @@
   },
   "dependencies": {
     "@astrojs/node": "^8.3.3",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "html-minifier": "^4.0.0"
   },
   "devDependencies": {
diff --git a/examples/minimal/package.json b/examples/minimal/package.json
index 8a892c29f4d9..e354465171db 100644
--- a/examples/minimal/package.json
+++ b/examples/minimal/package.json
@@ -11,6 +11,6 @@
     "astro": "astro"
   },
   "dependencies": {
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/non-html-pages/package.json b/examples/non-html-pages/package.json
index 0106f522117f..8b1af1116e23 100644
--- a/examples/non-html-pages/package.json
+++ b/examples/non-html-pages/package.json
@@ -11,6 +11,6 @@
     "astro": "astro"
   },
   "dependencies": {
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/portfolio/package.json b/examples/portfolio/package.json
index fb6256b22275..490e0a3b22db 100644
--- a/examples/portfolio/package.json
+++ b/examples/portfolio/package.json
@@ -11,6 +11,6 @@
     "astro": "astro"
   },
   "dependencies": {
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/server-islands/package.json b/examples/server-islands/package.json
index 86f7acb1a216..d9ecb186a368 100644
--- a/examples/server-islands/package.json
+++ b/examples/server-islands/package.json
@@ -17,7 +17,7 @@
     "@tailwindcss/forms": "^0.5.9",
     "@types/react": "^18.3.5",
     "@types/react-dom": "^18.3.0",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "postcss": "^8.4.45",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
diff --git a/examples/ssr/package.json b/examples/ssr/package.json
index 652197543d6c..9b1c4cb800a6 100644
--- a/examples/ssr/package.json
+++ b/examples/ssr/package.json
@@ -14,7 +14,7 @@
   "dependencies": {
     "@astrojs/node": "^8.3.3",
     "@astrojs/svelte": "^5.7.0",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "svelte": "^4.2.19"
   }
 }
diff --git a/examples/starlog/package.json b/examples/starlog/package.json
index 2886d3cb5ec0..378426cfb3fd 100644
--- a/examples/starlog/package.json
+++ b/examples/starlog/package.json
@@ -10,7 +10,7 @@
     "astro": "astro"
   },
   "dependencies": {
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "sass": "^1.78.0",
     "sharp": "^0.33.3"
   }
diff --git a/examples/toolbar-app/package.json b/examples/toolbar-app/package.json
index 6e452f1ada0a..beec943bbade 100644
--- a/examples/toolbar-app/package.json
+++ b/examples/toolbar-app/package.json
@@ -15,6 +15,6 @@
     "./app": "./dist/app.js"
   },
   "devDependencies": {
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/view-transitions/package.json b/examples/view-transitions/package.json
index 1563b1cb9e23..13484ffe7a9f 100644
--- a/examples/view-transitions/package.json
+++ b/examples/view-transitions/package.json
@@ -12,6 +12,6 @@
   "devDependencies": {
     "@astrojs/tailwind": "^5.1.0",
     "@astrojs/node": "^8.3.3",
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/with-markdoc/package.json b/examples/with-markdoc/package.json
index 94241cc27289..26a5afadc8d4 100644
--- a/examples/with-markdoc/package.json
+++ b/examples/with-markdoc/package.json
@@ -12,6 +12,6 @@
   },
   "dependencies": {
     "@astrojs/markdoc": "^0.11.4",
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/with-markdown-plugins/package.json b/examples/with-markdown-plugins/package.json
index fdc774ee1d26..bb472654ce94 100644
--- a/examples/with-markdown-plugins/package.json
+++ b/examples/with-markdown-plugins/package.json
@@ -12,7 +12,7 @@
   },
   "dependencies": {
     "@astrojs/markdown-remark": "^5.2.0",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "hast-util-select": "^6.0.2",
     "rehype-autolink-headings": "^7.1.0",
     "rehype-slug": "^6.0.0",
diff --git a/examples/with-markdown-shiki/package.json b/examples/with-markdown-shiki/package.json
index 420c6270d116..5b7beef2a275 100644
--- a/examples/with-markdown-shiki/package.json
+++ b/examples/with-markdown-shiki/package.json
@@ -11,6 +11,6 @@
     "astro": "astro"
   },
   "dependencies": {
-    "astro": "^4.15.4"
+    "astro": "^4.15.5"
   }
 }
diff --git a/examples/with-mdx/package.json b/examples/with-mdx/package.json
index 1b4e7cd4f745..290686f59c07 100644
--- a/examples/with-mdx/package.json
+++ b/examples/with-mdx/package.json
@@ -11,9 +11,9 @@
     "astro": "astro"
   },
   "dependencies": {
-    "@astrojs/mdx": "^3.1.5",
+    "@astrojs/mdx": "^3.1.6",
     "@astrojs/preact": "^3.5.3",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "preact": "^10.23.2"
   }
 }
diff --git a/examples/with-nanostores/package.json b/examples/with-nanostores/package.json
index 8706fad193b6..ea17f24b3c94 100644
--- a/examples/with-nanostores/package.json
+++ b/examples/with-nanostores/package.json
@@ -13,7 +13,7 @@
   "dependencies": {
     "@astrojs/preact": "^3.5.3",
     "@nanostores/preact": "^0.5.2",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "nanostores": "^0.11.3",
     "preact": "^10.23.2"
   }
diff --git a/examples/with-tailwindcss/package.json b/examples/with-tailwindcss/package.json
index 8f7995b45dbe..55a63847b455 100644
--- a/examples/with-tailwindcss/package.json
+++ b/examples/with-tailwindcss/package.json
@@ -11,10 +11,10 @@
     "astro": "astro"
   },
   "dependencies": {
-    "@astrojs/mdx": "^3.1.5",
+    "@astrojs/mdx": "^3.1.6",
     "@astrojs/tailwind": "^5.1.0",
     "@types/canvas-confetti": "^1.6.4",
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "autoprefixer": "^10.4.20",
     "canvas-confetti": "^1.9.3",
     "postcss": "^8.4.45",
diff --git a/examples/with-vitest/package.json b/examples/with-vitest/package.json
index 39f947259536..bd30c3df8b16 100644
--- a/examples/with-vitest/package.json
+++ b/examples/with-vitest/package.json
@@ -12,7 +12,7 @@
     "test": "vitest"
   },
   "dependencies": {
-    "astro": "^4.15.4",
+    "astro": "^4.15.5",
     "vitest": "^2.0.5"
   }
 }
diff --git a/packages/astro/CHANGELOG.md b/packages/astro/CHANGELOG.md
index 7853efb1650e..cfe6474f0cb8 100644
--- a/packages/astro/CHANGELOG.md
+++ b/packages/astro/CHANGELOG.md
@@ -1,5 +1,73 @@
 # astro
 
+## 4.15.5
+
+### Patch Changes
+
+- [#11939](https://github.com/withastro/astro/pull/11939) [`7b09c62`](https://github.com/withastro/astro/commit/7b09c62b565cd7b50c35fb68d390729f936a43fb) Thanks [@bholmesdev](https://github.com/bholmesdev)! - Adds support for Zod discriminated unions on Action form inputs. This allows forms with different inputs to be submitted to the same action, using a given input to decide which object should be used for validation.
+
+  This example accepts either a `create` or `update` form submission, and uses the `type` field to determine which object to validate against.
+
+  ```ts
+  import { defineAction } from 'astro:actions';
+  import { z } from 'astro:schema';
+
+  export const server = {
+    changeUser: defineAction({
+      accept: 'form',
+      input: z.discriminatedUnion('type', [
+        z.object({
+          type: z.literal('create'),
+          name: z.string(),
+          email: z.string().email(),
+        }),
+        z.object({
+          type: z.literal('update'),
+          id: z.number(),
+          name: z.string(),
+          email: z.string().email(),
+        }),
+      ]),
+      async handler(input) {
+        if (input.type === 'create') {
+          // input is { type: 'create', name: string, email: string }
+        } else {
+          // input is { type: 'update', id: number, name: string, email: string }
+        }
+      },
+    }),
+  };
+  ```
+
+  The corresponding `create` and `update` forms may look like this:
+
+  ```astro
+  ---
+  import { actions } from 'astro:actions';
+  ---
+
+  <!--Create-->
+  <form action={actions.changeUser} method="POST">
+    <input type="hidden" name="type" value="create" />
+    <input type="text" name="name" required />
+    <input type="email" name="email" required />
+    <button type="submit">Create User</button>
+  </form>
+
+  <!--Update-->
+  <form action={actions.changeUser} method="POST">
+    <input type="hidden" name="type" value="update" />
+    <input type="hidden" name="id" value="user-123" />
+    <input type="text" name="name" required />
+    <input type="email" name="email" required />
+    <button type="submit">Update User</button>
+  </form>
+  ```
+
+- [#11968](https://github.com/withastro/astro/pull/11968) [`86ad1fd`](https://github.com/withastro/astro/commit/86ad1fd223e2d2c448372caa159090efbee69237) Thanks [@NikolaRHristov](https://github.com/NikolaRHristov)! - Fixes a typo in the server island JSDoc
+
+- [#11983](https://github.com/withastro/astro/pull/11983) [`633eeaa`](https://github.com/withastro/astro/commit/633eeaa9d8a8a35bba638fde06fd8f52cc1c2ce3) Thanks [@uwej711](https://github.com/uwej711)! - Remove dependency on path-to-regexp
+
 ## 4.15.4
 
 ### Patch Changes
diff --git a/packages/astro/package.json b/packages/astro/package.json
index 11ad27c58c34..f3a2b7d0bbd0 100644
--- a/packages/astro/package.json
+++ b/packages/astro/package.json
@@ -1,6 +1,6 @@
 {
   "name": "astro",
-  "version": "4.15.4",
+  "version": "4.15.5",
   "description": "Astro is a modern site builder with web best practices, performance, and DX front-of-mind.",
   "type": "module",
   "author": "withastro",
@@ -168,7 +168,6 @@
     "ora": "^8.1.0",
     "p-limit": "^6.1.0",
     "p-queue": "^8.0.1",
-    "path-to-regexp": "^6.2.2",
     "preferred-pm": "^4.0.0",
     "prompts": "^2.4.2",
     "rehype": "^13.0.1",
diff --git a/packages/astro/src/@types/astro.ts b/packages/astro/src/@types/astro.ts
index 9087858f1115..41a874871941 100644
--- a/packages/astro/src/@types/astro.ts
+++ b/packages/astro/src/@types/astro.ts
@@ -2094,7 +2094,7 @@ export interface AstroUserConfig {
 		 *
 		 * The outer page will be rendered, either at build time (`hybrid`) or at runtime (`server`) with the island content omitted and a `<script>` tag included in its place.
 		 *
-		 * After the page loads in the browser, the script tag will replace itself with the the contents of the island by making a request.
+		 * After the page loads in the browser, the script tag will replace itself with the contents of the island by making a request.
 		 *
 		 * Any Astro component can be given the `server: defer` attribute to delay its rendering. There is no special API and you can write `.astro` code as normal:
 		 *
diff --git a/packages/astro/src/core/routing/manifest/generator.ts b/packages/astro/src/core/routing/manifest/generator.ts
index 4ab635ec6608..30758bfd1cab 100644
--- a/packages/astro/src/core/routing/manifest/generator.ts
+++ b/packages/astro/src/core/routing/manifest/generator.ts
@@ -1,7 +1,5 @@
 import type { AstroConfig, RoutePart } from '../../../@types/astro.js';
 
-import { compile } from 'path-to-regexp';
-
 /**
  * Sanitizes the parameters object by normalizing string values and replacing certain characters with their URL-encoded equivalents.
  * @param {Record<string, string | number | undefined>} params - The parameters object to be sanitized.
@@ -24,45 +22,40 @@ export function getRouteGenerator(
 	segments: RoutePart[][],
 	addTrailingSlash: AstroConfig['trailingSlash'],
 ) {
-	const template = segments
-		.map((segment) => {
-			return (
-				'/' +
-				segment
-					.map((part) => {
-						if (part.spread) {
-							return `:${part.content.slice(3)}(.*)?`;
-						} else if (part.dynamic) {
-							return `:${part.content}`;
-						} else {
-							return part.content
-								.normalize()
-								.replace(/\?/g, '%3F')
-								.replace(/#/g, '%23')
-								.replace(/%5B/g, '[')
-								.replace(/%5D/g, ']')
-								.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
-						}
-					})
-					.join('')
-			);
-		})
-		.join('');
-
-	// Unless trailingSlash config is set to 'always', don't automatically append it.
-	let trailing: '/' | '' = '';
-	if (addTrailingSlash === 'always' && segments.length) {
-		trailing = '/';
-	}
-	const toPath = compile(template + trailing);
 	return (params: Record<string, string | number | undefined>): string => {
 		const sanitizedParams = sanitizeParams(params);
-		const path = toPath(sanitizedParams);
 
-		// When generating an index from a rest parameter route, `path-to-regexp` will return an
-		// empty string instead "/". This causes an inconsistency with static indexes that may result
-		// in the incorrect routes being rendered.
-		// To fix this, we return "/" when the path is empty.
+		// Unless trailingSlash config is set to 'always', don't automatically append it.
+		let trailing: '/' | '' = '';
+		if (addTrailingSlash === 'always' && segments.length) {
+			trailing = '/';
+		}
+
+		const path =
+			segments
+				.map((segment) => {
+					return (
+						'/' +
+						segment
+							.map((part) => {
+								if (part.spread) {
+									return `${sanitizedParams[part.content.slice(3)] || ''}`;
+								} else if (part.dynamic) {
+									return `${sanitizedParams[part.content] || ''}`;
+								} else {
+									return part.content
+										.normalize()
+										.replace(/\?/g, '%3F')
+										.replace(/#/g, '%23')
+										.replace(/%5B/g, '[')
+										.replace(/%5D/g, ']');
+								}
+							})
+							.join('')
+					);
+				})
+				.join('') + trailing;
+
 		return path || '/';
 	};
 }
diff --git a/packages/integrations/mdx/CHANGELOG.md b/packages/integrations/mdx/CHANGELOG.md
index 1fe03c2eae00..59a99555e7eb 100644
--- a/packages/integrations/mdx/CHANGELOG.md
+++ b/packages/integrations/mdx/CHANGELOG.md
@@ -1,5 +1,11 @@
 # @astrojs/mdx
 
+## 3.1.6
+
+### Patch Changes
+
+- [#11975](https://github.com/withastro/astro/pull/11975) [`c9ae7b1`](https://github.com/withastro/astro/commit/c9ae7b1b89e050900bbc111f29e8c5d95c26bf36) Thanks [@bluwy](https://github.com/bluwy)! - Handles nested root hast node when optimizing MDX
+
 ## 3.1.5
 
 ### Patch Changes
diff --git a/packages/integrations/mdx/package.json b/packages/integrations/mdx/package.json
index 77a24527b0fc..aa7b25bf8e23 100644
--- a/packages/integrations/mdx/package.json
+++ b/packages/integrations/mdx/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@astrojs/mdx",
   "description": "Add support for MDX pages in your Astro site",
-  "version": "3.1.5",
+  "version": "3.1.6",
   "type": "module",
   "types": "./dist/index.d.ts",
   "author": "withastro",
diff --git a/packages/integrations/mdx/src/rehype-optimize-static.ts b/packages/integrations/mdx/src/rehype-optimize-static.ts
index 80c28ab9ca91..eba31cae0d11 100644
--- a/packages/integrations/mdx/src/rehype-optimize-static.ts
+++ b/packages/integrations/mdx/src/rehype-optimize-static.ts
@@ -64,8 +64,14 @@ export const rehypeOptimizeStatic: RehypePlugin<[OptimizeOptions?]> = (options)
 		 * A non-static node causes all its parents to be non-optimizable
 		 */
 		const isNodeNonStatic = (node: Node) => {
-			// @ts-expect-error Access `.tagName` naively for perf
-			return node.type.startsWith('mdx') || ignoreElementNames.has(node.tagName);
+			return (
+				node.type.startsWith('mdx') ||
+				// @ts-expect-error `node` should never have `type: 'root'`, but in some cases plugins may inject it as children,
+				// which MDX will render as a fragment instead (an MDX fragment is a `mdxJsxFlowElement` type).
+				node.type === 'root' ||
+				// @ts-expect-error Access `.tagName` naively for perf
+				ignoreElementNames.has(node.tagName)
+			);
 		};
 
 		visit(tree as any, {
diff --git a/packages/integrations/mdx/test/fixtures/mdx-optimize/astro.config.mjs b/packages/integrations/mdx/test/fixtures/mdx-optimize/astro.config.mjs
index 204549479f5d..a3626c3a3129 100644
--- a/packages/integrations/mdx/test/fixtures/mdx-optimize/astro.config.mjs
+++ b/packages/integrations/mdx/test/fixtures/mdx-optimize/astro.config.mjs
@@ -1,9 +1,37 @@
 import mdx from '@astrojs/mdx';
 
 export default {
-	integrations: [mdx({
-		optimize: {
-			ignoreElementNames: ['strong']
-		}
-	})]
-}
+	integrations: [
+		mdx({
+			optimize: {
+				ignoreElementNames: ['strong'],
+			},
+		}),
+	],
+	markdown: {
+		rehypePlugins: [
+			() => {
+				return (tree) => {
+					tree.children.push({
+						type: 'root',
+						children: [
+							{
+								type: 'element',
+								tagName: 'p',
+								properties: {
+									id: 'injected-root-hast',
+								},
+								children: [
+									{
+										type: 'text',
+										value: 'Injected root hast from rehype plugin',
+									},
+								],
+							},
+						],
+					});
+				};
+			},
+		],
+	},
+};
diff --git a/packages/integrations/mdx/test/mdx-optimize.test.js b/packages/integrations/mdx/test/mdx-optimize.test.js
index 47acfdff80ce..c45ecda15015 100644
--- a/packages/integrations/mdx/test/mdx-optimize.test.js
+++ b/packages/integrations/mdx/test/mdx-optimize.test.js
@@ -47,4 +47,15 @@ describe('MDX optimize', () => {
 		assert.notEqual(blockquote, null);
 		assert.equal(blockquote.textContent.includes('I like pancakes'), true);
 	});
+
+	it('renders MDX with rehype plugin that incorrectly injects root hast node', async () => {
+		const html = await fixture.readFile('/import/index.html');
+		const { document } = parseHTML(html);
+
+		assert.doesNotMatch(html, /set:html=/);
+		assert.equal(
+			document.getElementById('injected-root-hast').textContent,
+			'Injected root hast from rehype plugin',
+		);
+	});
 });
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9937787d9940..3f7eebdf61b7 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -116,13 +116,13 @@ importers:
   examples/basics:
     dependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/blog:
     dependencies:
       '@astrojs/mdx':
-        specifier: ^3.1.5
+        specifier: ^3.1.6
         version: link:../../packages/integrations/mdx
       '@astrojs/rss':
         specifier: ^4.0.7
@@ -131,13 +131,13 @@ importers:
         specifier: ^3.1.6
         version: link:../../packages/integrations/sitemap
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/component:
     devDependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/container-with-vitest:
@@ -146,7 +146,7 @@ importers:
         specifier: ^3.6.2
         version: link:../../packages/integrations/react
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       react:
         specifier: ^18.3.1
@@ -177,7 +177,7 @@ importers:
         specifier: ^3.14.1
         version: 3.14.1
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/framework-lit:
@@ -189,7 +189,7 @@ importers:
         specifier: ^0.2.1
         version: 0.2.1
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       lit:
         specifier: ^3.2.0
@@ -219,7 +219,7 @@ importers:
         specifier: ^18.3.0
         version: 18.3.0
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       preact:
         specifier: ^10.23.2
@@ -249,7 +249,7 @@ importers:
         specifier: ^1.3.0
         version: 1.3.0(preact@10.23.2)
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       preact:
         specifier: ^10.23.2
@@ -267,7 +267,7 @@ importers:
         specifier: ^18.3.0
         version: 18.3.0
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       react:
         specifier: ^18.3.1
@@ -282,7 +282,7 @@ importers:
         specifier: ^4.4.1
         version: link:../../packages/integrations/solid
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       solid-js:
         specifier: ^1.8.22
@@ -294,7 +294,7 @@ importers:
         specifier: ^5.7.0
         version: link:../../packages/integrations/svelte
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       svelte:
         specifier: ^4.2.19
@@ -306,7 +306,7 @@ importers:
         specifier: ^4.5.0
         version: link:../../packages/integrations/vue
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       vue:
         specifier: ^3.5.3
@@ -318,13 +318,13 @@ importers:
         specifier: ^8.3.3
         version: 8.3.3(astro@packages+astro)
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/integration:
     devDependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/middleware:
@@ -333,7 +333,7 @@ importers:
         specifier: ^8.3.3
         version: 8.3.3(astro@packages+astro)
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       html-minifier:
         specifier: ^4.0.0
@@ -346,19 +346,19 @@ importers:
   examples/minimal:
     dependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/non-html-pages:
     dependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/portfolio:
     dependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/server-islands:
@@ -385,7 +385,7 @@ importers:
         specifier: ^18.3.0
         version: 18.3.0
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       postcss:
         specifier: ^8.4.45
@@ -409,7 +409,7 @@ importers:
         specifier: ^5.7.0
         version: link:../../packages/integrations/svelte
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       svelte:
         specifier: ^4.2.19
@@ -418,7 +418,7 @@ importers:
   examples/starlog:
     dependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       sass:
         specifier: ^1.78.0
@@ -430,7 +430,7 @@ importers:
   examples/toolbar-app:
     devDependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/view-transitions:
@@ -442,7 +442,7 @@ importers:
         specifier: ^5.1.0
         version: link:../../packages/integrations/tailwind
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/with-markdoc:
@@ -451,7 +451,7 @@ importers:
         specifier: ^0.11.4
         version: link:../../packages/integrations/markdoc
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/with-markdown-plugins:
@@ -460,7 +460,7 @@ importers:
         specifier: ^5.2.0
         version: link:../../packages/markdown/remark
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       hast-util-select:
         specifier: ^6.0.2
@@ -481,19 +481,19 @@ importers:
   examples/with-markdown-shiki:
     dependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
 
   examples/with-mdx:
     dependencies:
       '@astrojs/mdx':
-        specifier: ^3.1.5
+        specifier: ^3.1.6
         version: link:../../packages/integrations/mdx
       '@astrojs/preact':
         specifier: ^3.5.3
         version: link:../../packages/integrations/preact
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       preact:
         specifier: ^10.23.2
@@ -508,7 +508,7 @@ importers:
         specifier: ^0.5.2
         version: 0.5.2(nanostores@0.11.3)(preact@10.23.2)
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       nanostores:
         specifier: ^0.11.3
@@ -520,7 +520,7 @@ importers:
   examples/with-tailwindcss:
     dependencies:
       '@astrojs/mdx':
-        specifier: ^3.1.5
+        specifier: ^3.1.6
         version: link:../../packages/integrations/mdx
       '@astrojs/tailwind':
         specifier: ^5.1.0
@@ -529,7 +529,7 @@ importers:
         specifier: ^1.6.4
         version: 1.6.4
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       autoprefixer:
         specifier: ^10.4.20
@@ -547,7 +547,7 @@ importers:
   examples/with-vitest:
     dependencies:
       astro:
-        specifier: ^4.15.4
+        specifier: ^4.15.5
         version: link:../../packages/astro
       vitest:
         specifier: ^2.0.5
@@ -693,9 +693,6 @@ importers:
       p-queue:
         specifier: ^8.0.1
         version: 8.0.1
-      path-to-regexp:
-        specifier: ^6.2.2
-        version: 6.2.2
       preferred-pm:
         specifier: ^4.0.0
         version: 4.0.0
@@ -8865,12 +8862,10 @@ packages:
 
   libsql@0.3.19:
     resolution: {integrity: sha512-Aj5cQ5uk/6fHdmeW0TiXK42FqUlwx7ytmMLPSaUQPin5HKKKuUPD62MAbN4OEweGBBI7q1BekoEN4gPUEL6MZA==}
-    cpu: [x64, arm64, wasm32]
     os: [darwin, linux, win32]
 
   libsql@0.4.1:
     resolution: {integrity: sha512-qZlR9Yu1zMBeLChzkE/cKfoKV3Esp9cn9Vx5Zirn4AVhDWPcjYhKwbtJcMuHehgk3mH+fJr9qW+3vesBWbQpBg==}
-    cpu: [x64, arm64, wasm32]
     os: [darwin, linux, win32]
 
   lilconfig@2.1.0:
@@ -9548,9 +9543,6 @@ packages:
     resolution: {integrity: sha512-7xTavNy5RQXnsjANvVvMkEjvloOinkAjv/Z6Ildz9v2RinZ4SBKTWFOVRbaF8p0vpHnyjV/UwNDdKuUv6M5qcA==}
     engines: {node: '>=16 || 14 >=14.17'}
 
-  path-to-regexp@6.2.2:
-    resolution: {integrity: sha512-GQX3SSMokngb36+whdpRXE+3f9V8UzyAorlYvOGx87ufGHehNTn5lCxrKtLyZ4Yl/wEKnNnr98ZzOwwDZV5ogw==}
-
   path-type@4.0.0:
     resolution: {integrity: sha512-gDKb8aZMDeD/tZWs9P6+q0J9Mwkdl6xMV8TjnGP3qJVJ06bdMgkbBlLU8IdfOsIsFz2BW1rNVT3XuNEl8zPAvw==}
     engines: {node: '>=8'}
@@ -15584,8 +15576,6 @@ snapshots:
       lru-cache: 10.2.0
       minipass: 7.1.2
 
-  path-to-regexp@6.2.2: {}
-
   path-type@4.0.0: {}
 
   path-type@5.0.0: {}