diff --git a/.github/workflows/test-cache.yml b/.github/workflows/test-cache.yml
index 93dcb69..a6c9ada 100644
--- a/.github/workflows/test-cache.yml
+++ b/.github/workflows/test-cache.yml
@@ -214,3 +214,14 @@ jobs:
       - name: Remove cache dependency glob file
         run: rm -f ~/uv-cache.glob
         shell: bash
+
+  test-no-python-version:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Setup with cache
+        uses: ./
+        with:
+          enable-cache: true
+      - run: uv sync
+        working-directory: __tests__/fixtures/old-python-constraint-project
diff --git a/__tests__/fixtures/old-python-constraint-project/README.md b/__tests__/fixtures/old-python-constraint-project/README.md
new file mode 100644
index 0000000..e69de29
diff --git a/__tests__/fixtures/old-python-constraint-project/pyproject.toml b/__tests__/fixtures/old-python-constraint-project/pyproject.toml
new file mode 100644
index 0000000..0d381bb
--- /dev/null
+++ b/__tests__/fixtures/old-python-constraint-project/pyproject.toml
@@ -0,0 +1,13 @@
+[project]
+name = "old-python-constraint-project"
+version = "0.1.0"
+description = "Add your description here"
+readme = "README.md"
+requires-python = ">=3.8,<=3.9"
+dependencies = [
+    "ruff>=0.6.2",
+]
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
diff --git a/__tests__/fixtures/old-python-constraint-project/src/old_python_constraint_project/__init__.py b/__tests__/fixtures/old-python-constraint-project/src/old_python_constraint_project/__init__.py
new file mode 100644
index 0000000..94ebc9c
--- /dev/null
+++ b/__tests__/fixtures/old-python-constraint-project/src/old_python_constraint_project/__init__.py
@@ -0,0 +1,2 @@
+def hello() -> str:
+    return "Hello from uv-project!"
diff --git a/__tests__/fixtures/old-python-constraint-project/uv.lock b/__tests__/fixtures/old-python-constraint-project/uv.lock
new file mode 100644
index 0000000..3838f8c
--- /dev/null
+++ b/__tests__/fixtures/old-python-constraint-project/uv.lock
@@ -0,0 +1,38 @@
+version = 1
+requires-python = ">=3.12"
+
+[[package]]
+name = "ruff"
+version = "0.6.2"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/23/f4/279d044f66b79261fd37df76bf72b64471afab5d3b7906a01499c4451910/ruff-0.6.2.tar.gz", hash = "sha256:239ee6beb9e91feb8e0ec384204a763f36cb53fb895a1a364618c6abb076b3be", size = 2460281 }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/72/4b/47dd7a69287afb4069fa42c198e899463605460a58120196711bfcf0446b/ruff-0.6.2-py3-none-linux_armv6l.whl", hash = "sha256:5c8cbc6252deb3ea840ad6a20b0f8583caab0c5ef4f9cca21adc5a92b8f79f3c", size = 9695871 },
+    { url = "https://files.pythonhosted.org/packages/ae/c3/8aac62ac4638c14a740ee76a755a925f2d0d04580ab790a9887accb729f6/ruff-0.6.2-py3-none-macosx_10_12_x86_64.whl", hash = "sha256:17002fe241e76544448a8e1e6118abecbe8cd10cf68fde635dad480dba594570", size = 9459354 },
+    { url = "https://files.pythonhosted.org/packages/2f/cf/77fbd8d4617b9b9c503f9bffb8552c4e3ea1a58dc36975e7a9104ffb0f85/ruff-0.6.2-py3-none-macosx_11_0_arm64.whl", hash = "sha256:3dbeac76ed13456f8158b8f4fe087bf87882e645c8e8b606dd17b0b66c2c1158", size = 9163871 },
+    { url = "https://files.pythonhosted.org/packages/05/1c/765192bab32b79efbb498b06f0b9dcb3629112b53b8777ae1d19b8209e09/ruff-0.6.2-py3-none-manylinux_2_17_aarch64.manylinux2014_aarch64.whl", hash = "sha256:094600ee88cda325988d3f54e3588c46de5c18dae09d683ace278b11f9d4d534", size = 10096250 },
+    { url = "https://files.pythonhosted.org/packages/08/d0/86f3cb0f6934c99f759c232984a5204d67a26745cad2d9edff6248adf7d2/ruff-0.6.2-py3-none-manylinux_2_17_armv7l.manylinux2014_armv7l.whl", hash = "sha256:316d418fe258c036ba05fbf7dfc1f7d3d4096db63431546163b472285668132b", size = 9475376 },
+    { url = "https://files.pythonhosted.org/packages/cd/cc/4c8d0e225b559a3fae6092ec310d7150d3b02b4669e9223f783ef64d82c0/ruff-0.6.2-py3-none-manylinux_2_17_i686.manylinux2014_i686.whl", hash = "sha256:d72b8b3abf8a2d51b7b9944a41307d2f442558ccb3859bbd87e6ae9be1694a5d", size = 10295634 },
+    { url = "https://files.pythonhosted.org/packages/db/96/d2699cfb1bb5a01c68122af43454c76c31331e1c8a9bd97d653d7c82524b/ruff-0.6.2-py3-none-manylinux_2_17_ppc64.manylinux2014_ppc64.whl", hash = "sha256:2aed7e243be68487aa8982e91c6e260982d00da3f38955873aecd5a9204b1d66", size = 11024941 },
+    { url = "https://files.pythonhosted.org/packages/8b/a9/6ecd66af8929e0f2a1ed308a4137f3521789f28f0eb97d32c2ca3aa7000c/ruff-0.6.2-py3-none-manylinux_2_17_ppc64le.manylinux2014_ppc64le.whl", hash = "sha256:d371f7fc9cec83497fe7cf5eaf5b76e22a8efce463de5f775a1826197feb9df8", size = 10606894 },
+    { url = "https://files.pythonhosted.org/packages/e4/73/2ee4cd19f44992fedac1cc6db9e3d825966072f6dcbd4032f21cbd063170/ruff-0.6.2-py3-none-manylinux_2_17_s390x.manylinux2014_s390x.whl", hash = "sha256:a8f310d63af08f583363dfb844ba8f9417b558199c58a5999215082036d795a1", size = 11552886 },
+    { url = "https://files.pythonhosted.org/packages/60/4c/c0f1cd35ce4a93c54a6bb1ee6934a3a205fa02198dd076678193853ceea1/ruff-0.6.2-py3-none-manylinux_2_17_x86_64.manylinux2014_x86_64.whl", hash = "sha256:7db6880c53c56addb8638fe444818183385ec85eeada1d48fc5abe045301b2f1", size = 10264945 },
+    { url = "https://files.pythonhosted.org/packages/c4/89/e45c9359b9cdd4245512ea2b9f2bb128a997feaa5f726fc9e8c7a66afadf/ruff-0.6.2-py3-none-musllinux_1_2_aarch64.whl", hash = "sha256:1175d39faadd9a50718f478d23bfc1d4da5743f1ab56af81a2b6caf0a2394f23", size = 10100007 },
+    { url = "https://files.pythonhosted.org/packages/06/74/0bd4e0a7ed5f6908df87892f9bf60a2356c0fd74102d8097298bd9b4f346/ruff-0.6.2-py3-none-musllinux_1_2_armv7l.whl", hash = "sha256:5b939f9c86d51635fe486585389f54582f0d65b8238e08c327c1534844b3bb9a", size = 9559267 },
+    { url = "https://files.pythonhosted.org/packages/54/03/3dc6dc9419f276f05805bf888c279e3e0b631284abd548d9e87cebb93aec/ruff-0.6.2-py3-none-musllinux_1_2_i686.whl", hash = "sha256:d0d62ca91219f906caf9b187dea50d17353f15ec9bb15aae4a606cd697b49b4c", size = 9905304 },
+    { url = "https://files.pythonhosted.org/packages/5c/5b/d6a72a6a6bbf097c09de468326ef5fa1c9e7aa5e6e45979bc0d984b0dbe7/ruff-0.6.2-py3-none-musllinux_1_2_x86_64.whl", hash = "sha256:7438a7288f9d67ed3c8ce4d059e67f7ed65e9fe3aa2ab6f5b4b3610e57e3cb56", size = 10341480 },
+    { url = "https://files.pythonhosted.org/packages/79/a9/0f2f21fe15ba537c46598f96aa9ae4a3d4b9ec64926664617ca6a8c772f4/ruff-0.6.2-py3-none-win32.whl", hash = "sha256:279d5f7d86696df5f9549b56b9b6a7f6c72961b619022b5b7999b15db392a4da", size = 7961901 },
+    { url = "https://files.pythonhosted.org/packages/b0/80/fff12ffe11853d9f4ea3e5221e6dd2e93640a161c05c9579833e09ad40a7/ruff-0.6.2-py3-none-win_amd64.whl", hash = "sha256:d9f3469c7dd43cd22eb1c3fc16926fb8258d50cb1b216658a07be95dd117b0f2", size = 8783320 },
+    { url = "https://files.pythonhosted.org/packages/56/91/577cdd64cce5e74d3f8b5ecb93f29566def569c741eb008aed4f331ef821/ruff-0.6.2-py3-none-win_arm64.whl", hash = "sha256:f28fcd2cd0e02bdf739297516d5643a945cc7caf09bd9bcb4d932540a5ea4fa9", size = 8225886 },
+]
+
+[[package]]
+name = "uv-project"
+version = "0.1.0"
+source = { editable = "." }
+dependencies = [
+    { name = "ruff" },
+]
+
+[package.metadata]
+requires-dist = [{ name = "ruff" }]
diff --git a/dist/save-cache/index.js b/dist/save-cache/index.js
index 5bae647..93af54d 100644
--- a/dist/save-cache/index.js
+++ b/dist/save-cache/index.js
@@ -91461,6 +91461,7 @@ const core = __importStar(__nccwpck_require__(7484));
 const inputs_1 = __nccwpck_require__(9612);
 const platforms_1 = __nccwpck_require__(8361);
 const hash_files_1 = __nccwpck_require__(9660);
+const exec = __importStar(__nccwpck_require__(5236));
 exports.STATE_CACHE_KEY = "cache-key";
 exports.STATE_CACHE_MATCHED_KEY = "cache-matched-key";
 const CACHE_VERSION = "1";
@@ -91496,7 +91497,30 @@ function computeKeys(version) {
             cacheDependencyPathHash += "no-dependency-glob";
         }
         const suffix = inputs_1.cacheSuffix ? `-${inputs_1.cacheSuffix}` : "";
-        return `setup-uv-${CACHE_VERSION}-${(0, platforms_1.getArch)()}-${(0, platforms_1.getPlatform)()}-${version}${cacheDependencyPathHash}${suffix}`;
+        const pythonVersion = yield getPythonVersion();
+        return `setup-uv-${CACHE_VERSION}-${(0, platforms_1.getArch)()}-${(0, platforms_1.getPlatform)()}-${version}-${pythonVersion}${cacheDependencyPathHash}${suffix}`;
+    });
+}
+function getPythonVersion() {
+    return __awaiter(this, void 0, void 0, function* () {
+        if (inputs_1.pythonVersion !== "") {
+            return inputs_1.pythonVersion;
+        }
+        const options = {
+            silent: !core.isDebug(),
+        };
+        const execArgs = ["python", "find"];
+        let output = "";
+        options.listeners = {
+            stdout: (data) => {
+                output += data.toString();
+            },
+        };
+        yield exec.exec("uv", execArgs, options);
+        const pythonPath = output.trim();
+        output = "";
+        yield exec.exec(pythonPath, ["--version"], options);
+        return output.trim();
     });
 }
 function handleMatchResult(matchedKey, primaryKey) {
diff --git a/dist/setup/index.js b/dist/setup/index.js
index 0452816..d4d3f9d 100644
--- a/dist/setup/index.js
+++ b/dist/setup/index.js
@@ -96544,6 +96544,7 @@ const core = __importStar(__nccwpck_require__(7484));
 const inputs_1 = __nccwpck_require__(9612);
 const platforms_1 = __nccwpck_require__(8361);
 const hash_files_1 = __nccwpck_require__(9660);
+const exec = __importStar(__nccwpck_require__(5236));
 exports.STATE_CACHE_KEY = "cache-key";
 exports.STATE_CACHE_MATCHED_KEY = "cache-matched-key";
 const CACHE_VERSION = "1";
@@ -96579,7 +96580,30 @@ function computeKeys(version) {
             cacheDependencyPathHash += "no-dependency-glob";
         }
         const suffix = inputs_1.cacheSuffix ? `-${inputs_1.cacheSuffix}` : "";
-        return `setup-uv-${CACHE_VERSION}-${(0, platforms_1.getArch)()}-${(0, platforms_1.getPlatform)()}-${version}${cacheDependencyPathHash}${suffix}`;
+        const pythonVersion = yield getPythonVersion();
+        return `setup-uv-${CACHE_VERSION}-${(0, platforms_1.getArch)()}-${(0, platforms_1.getPlatform)()}-${version}-${pythonVersion}${cacheDependencyPathHash}${suffix}`;
+    });
+}
+function getPythonVersion() {
+    return __awaiter(this, void 0, void 0, function* () {
+        if (inputs_1.pythonVersion !== "") {
+            return inputs_1.pythonVersion;
+        }
+        const options = {
+            silent: !core.isDebug(),
+        };
+        const execArgs = ["python", "find"];
+        let output = "";
+        options.listeners = {
+            stdout: (data) => {
+                output += data.toString();
+            },
+        };
+        yield exec.exec("uv", execArgs, options);
+        const pythonPath = output.trim();
+        output = "";
+        yield exec.exec(pythonPath, ["--version"], options);
+        return output.trim();
     });
 }
 function handleMatchResult(matchedKey, primaryKey) {
diff --git a/src/cache/restore-cache.ts b/src/cache/restore-cache.ts
index 134b98b..20288d1 100644
--- a/src/cache/restore-cache.ts
+++ b/src/cache/restore-cache.ts
@@ -4,9 +4,11 @@ import {
   cacheDependencyGlob,
   cacheLocalPath,
   cacheSuffix,
+  pythonVersion as pythonVersionInput,
 } from "../utils/inputs";
 import { getArch, getPlatform } from "../utils/platforms";
 import { hashFiles } from "../hash/hash-files";
+import * as exec from "@actions/exec";
 
 export const STATE_CACHE_KEY = "cache-key";
 export const STATE_CACHE_MATCHED_KEY = "cache-matched-key";
@@ -49,7 +51,31 @@ async function computeKeys(version: string): Promise<string> {
     cacheDependencyPathHash += "no-dependency-glob";
   }
   const suffix = cacheSuffix ? `-${cacheSuffix}` : "";
-  return `setup-uv-${CACHE_VERSION}-${getArch()}-${getPlatform()}-${version}${cacheDependencyPathHash}${suffix}`;
+  const pythonVersion = await getPythonVersion();
+  return `setup-uv-${CACHE_VERSION}-${getArch()}-${getPlatform()}-${version}-${pythonVersion}${cacheDependencyPathHash}${suffix}`;
+}
+
+async function getPythonVersion(): Promise<string> {
+  if (pythonVersionInput !== "") {
+    return pythonVersionInput;
+  }
+
+  const options: exec.ExecOptions = {
+    silent: !core.isDebug(),
+  };
+  const execArgs = ["python", "find"];
+
+  let output = "";
+  options.listeners = {
+    stdout: (data: Buffer) => {
+      output += data.toString();
+    },
+  };
+  await exec.exec("uv", execArgs, options);
+  const pythonPath = output.trim();
+  output = "";
+  await exec.exec(pythonPath, ["--version"], options);
+  return output.trim();
 }
 
 function handleMatchResult(