diff --git a/apps/tests/src/e2e/api-call.test.ts b/apps/tests/src/e2e/api-call.test.ts
index dea2403c3..07dbd2a82 100644
--- a/apps/tests/src/e2e/api-call.test.ts
+++ b/apps/tests/src/e2e/api-call.test.ts
@@ -5,4 +5,18 @@ test.describe("api calls", () => {
     const response = await fetch("http://localhost:3000/api/text-plain");
     expect(await response.text()).toBe("test");
   });
+
+  test("should include headers from both event and returned request", async () => {
+    const okResp = await fetch("http://localhost:3000/api/header-merging?status=ok");
+    expect(okResp.headers.get("Set-Cookie")).toBeTruthy();
+    expect(okResp.headers.get("x-event-header")).toBe("value");
+    expect(okResp.headers.get("x-return-header")).toBe("value");
+    expect(okResp.headers.get("x-shared-header")).toBe("event");
+
+    const redirectResp = await fetch("http://localhost:3000/api/header-merging?status=redirect", { redirect: "manual" });
+    expect(redirectResp.headers.get("Set-Cookie")).toBeTruthy();
+    expect(redirectResp.headers.get("x-event-header")).toBe("value");
+    expect(redirectResp.headers.get("x-return-header")).toBe("value");
+    expect(redirectResp.headers.get("x-shared-header")).toBe("event");
+  })
 });
diff --git a/apps/tests/src/routes/api/header-merging.ts b/apps/tests/src/routes/api/header-merging.ts
new file mode 100644
index 000000000..0b85a77ea
--- /dev/null
+++ b/apps/tests/src/routes/api/header-merging.ts
@@ -0,0 +1,29 @@
+import { getRequestURL, setHeader, useSession } from "@solidjs/start/http";
+
+export async function GET() {
+  const url = getRequestURL();
+
+  const s = await useSession({ password: "0".repeat(32) });
+  await s.update(d => ({count: (d.count || 0) + 1}))
+
+  setHeader("x-event-header", "value");
+  setHeader("x-shared-header", "event");
+
+  if(url.searchParams.get("status") === "redirect") {
+    return new Response(null, {
+      status: 301,
+      headers: {
+        location: "http://::/abc",
+        "x-return-header": "value",
+        "x-shared-header": "return"
+      }
+    })
+  } else {
+    return new Response(null, {
+      headers: {
+        "x-return-header": "value",
+        "x-shared-header": "return"
+      }
+    })
+  }
+}
diff --git a/packages/start/src/server/handler.ts b/packages/start/src/server/handler.ts
index 58d69aa87..cdcacc600 100644
--- a/packages/start/src/server/handler.ts
+++ b/packages/start/src/server/handler.ts
@@ -38,7 +38,8 @@ export function createBaseHandler(
 			if (pathname.startsWith(serverFunctionTest)) {
 				const serverFnResponse = await handleServerFunction(e);
 
-				if (serverFnResponse instanceof Response) return serverFnResponse;
+        if (serverFnResponse instanceof Response)
+          return produceResponseWithEventHeaders(serverFnResponse);
 
 				return new Response(serverFnResponse as any, {
 					headers: e.res.headers,
@@ -56,7 +57,11 @@ export function createBaseHandler(
 				// @ts-expect-error
 				sharedConfig.context = { event };
 				const res = await fn!(event);
-				if (res !== undefined) return res;
+        if (res !== undefined) {
+          if(res instanceof Response) return produceResponseWithEventHeaders(res)
+
+          return res;
+        }
 				if (event.request.method !== "GET") {
 					throw new Error(
 						`API handler for ${event.request.method} "${event.request.url}" did not return a response.`,
@@ -130,7 +135,7 @@ export function createBaseHandler(
 
 	const app = new H3();
 
-	app.use(handler);
+  app.use(handler);
 
 	return app;
 }
@@ -222,3 +227,24 @@ function handleStreamCompleteRedirect(context: PageEvent) {
     to && write(`<script>window.location="${to}"</script>`);
   };
 }
+
+function produceResponseWithEventHeaders(res: Response) {
+  const event = getRequestEvent()!;
+
+  let ret = res;
+
+  // Response.redirect returns an immutable value, so we clone on any redirect just in case
+  if(300 <= res.status && res.status < 400) {
+    ret = new Response(res.body, {
+      status: res.status,
+      statusText: res.statusText,
+      headers: Object.fromEntries(res.headers.entries())
+    });
+  }
+
+  for(const [name, value] of event.response.headers) {
+    ret.headers.set(name, value);
+  }
+
+  return ret
+}