diff --git a/packages/socket.io-client/support/rollup.config.esm.js b/packages/socket.io-client/support/rollup.config.esm.js
index 9105ec0cc5..ce54060c23 100644
--- a/packages/socket.io-client/support/rollup.config.esm.js
+++ b/packages/socket.io-client/support/rollup.config.esm.js
@@ -15,7 +15,15 @@ module.exports = {
     file: "./dist/socket.io.esm.min.js",
     format: "esm",
     sourcemap: true,
-    plugins: [terser()],
+    plugins: [
+      terser({
+        mangle: {
+          properties: {
+            regex: /^_/,
+          },
+        },
+      }),
+    ],
     banner,
   },
   plugins: [
diff --git a/packages/socket.io-client/support/rollup.config.umd.js b/packages/socket.io-client/support/rollup.config.umd.js
index 2d279111e3..0d83056d77 100644
--- a/packages/socket.io-client/support/rollup.config.umd.js
+++ b/packages/socket.io-client/support/rollup.config.umd.js
@@ -47,7 +47,15 @@ const prodBundle = {
     format: "umd",
     name: "io",
     sourcemap: true,
-    plugins: [terser()],
+    plugins: [
+      terser({
+        mangle: {
+          properties: {
+            regex: /^_/,
+          },
+        },
+      }),
+    ],
     banner,
   },
   plugins: [