diff --git a/packages/astro/package.json b/packages/astro/package.json
index 370cd8bee29d..4539479195a0 100644
--- a/packages/astro/package.json
+++ b/packages/astro/package.json
@@ -33,7 +33,7 @@
       "require": "./build/cjs/index.server.js"
     },
     "./middleware": {
-      "types": "./build/types/integration/middleware/index.types.d.ts",
+      "types": "./build/types/integration/middleware/index.d.ts",
       "node": "./build/esm/integration/middleware/index.js",
       "import": "./build/esm/integration/middleware/index.js",
       "require": "./build/cjs/integration/middleware/index.js"
diff --git a/packages/astro/src/integration/middleware/index.ts b/packages/astro/src/integration/middleware/index.ts
index 46c7ad9531b5..0208290c2733 100644
--- a/packages/astro/src/integration/middleware/index.ts
+++ b/packages/astro/src/integration/middleware/index.ts
@@ -1,6 +1,8 @@
-import type { MiddlewareResponseHandler } from 'astro';
 import { handleRequest } from '../../server/middleware';
 
+type MiddlewareNext = () => Promise<Response>;
+type MiddlewareHandler = (ctx: unknown, next: MiddlewareNext) => Promise<Response> | Response | Promise<void> | void;
+
 /**
  * This export is used by our integration to automatically add the middleware
  * to astro ^3.5.0 projects.
@@ -10,6 +12,13 @@ import { handleRequest } from '../../server/middleware';
  * middleware registration in our integration and manually add it in their own
  * `/src/middleware.js` file.
  */
-export const onRequest: MiddlewareResponseHandler = (ctx, next) => {
-  return handleRequest()(ctx, next);
+export const onRequest: MiddlewareHandler = (ctx, next) => {
+  const middleware = handleRequest();
+
+  // `onRequest` deliberately uses framework-agnostic parameter types so the published
+  // `@sentry/astro/middleware` declaration does not reference Astro-version-specific types
+  // (e.g. `MiddlewareResponseHandler`, which is absent in some supported Astro versions).
+  // The handler returned by `handleRequest()` is typed against Astro's own types, so we cast
+  // back to its expected parameter types here – the runtime shapes are identical.
+  return middleware(ctx as Parameters<typeof middleware>[0], next as Parameters<typeof middleware>[1]);
 };
diff --git a/packages/astro/test/integration/middleware/index.test-d.ts b/packages/astro/test/integration/middleware/index.test-d.ts
new file mode 100644
index 000000000000..5f482f98746e
--- /dev/null
+++ b/packages/astro/test/integration/middleware/index.test-d.ts
@@ -0,0 +1,18 @@
+import { describe, expectTypeOf, it } from 'vitest';
+import { onRequest } from '../../../src/integration/middleware';
+
+describe('Integration middleware types', () => {
+  // Regression test for #21413: the published `@sentry/astro/middleware` declaration must stay
+  // framework-agnostic. Typing `onRequest` against Astro-version-specific aliases (such as
+  // `MiddlewareResponseHandler`) made the public type depend on an export that is absent in some
+  // supported Astro versions. The assertions below fail on that previous typing and pass with the fix.
+  it('exposes onRequest as a framework-agnostic middleware handler', () => {
+    expectTypeOf(onRequest).toBeFunction();
+    expectTypeOf(onRequest).parameters.toEqualTypeOf<[unknown, () => Promise<Response>]>();
+    expectTypeOf(onRequest).returns.toEqualTypeOf<Promise<Response> | Response | Promise<void> | void>();
+  });
+
+  it('is callable with a minimal context and a zero-argument next', () => {
+    expectTypeOf(onRequest).toBeCallableWith({}, () => Promise.resolve(new Response()));
+  });
+});
diff --git a/packages/astro/test/integration/middleware/index.test.ts b/packages/astro/test/integration/middleware/index.test.ts
index 2a63a66027e8..1ce7b8d8e9b9 100644
--- a/packages/astro/test/integration/middleware/index.test.ts
+++ b/packages/astro/test/integration/middleware/index.test.ts
@@ -24,7 +24,7 @@ describe('Integration middleware', () => {
         id: '123',
       },
     };
-    // @ts-expect-error - a partial ctx object is fine here
+    // `onRequest` accepts a framework-agnostic `ctx`, so a partial Astro context is fine here.
     const res = await onRequest(ctx, next);
 
     expect(res).toBeDefined();