diff --git a/.changeset/blue-planets-juggle.md b/.changeset/blue-planets-juggle.md
new file mode 100644
index 00000000000..c740d1918de
--- /dev/null
+++ b/.changeset/blue-planets-juggle.md
@@ -0,0 +1,5 @@
+---
+'@apollo/server': patch
+---
+
+Allow case insensitive lookup on headers. Use HeaderMap instead of plain Map for headers in expressMiddleware.
diff --git a/packages/server/src/express4/index.ts b/packages/server/src/express4/index.ts
index 6dd8971c216..90bab238439 100644
--- a/packages/server/src/express4/index.ts
+++ b/packages/server/src/express4/index.ts
@@ -7,6 +7,7 @@ import type {
   HTTPGraphQLRequest,
 } from '../externalTypes/index.js';
 import { parse as urlParse } from 'url';
+import { HeaderMap } from '../utils/HeaderMap.js';
 
 export interface ExpressContextFunctionArgument {
   req: express.Request;
@@ -56,7 +57,7 @@ export function expressMiddleware<TContext extends BaseContext>(
       return;
     }
 
-    const headers = new Map<string, string>();
+    const headers = new HeaderMap();
     for (const [key, value] of Object.entries(req.headers)) {
       if (value !== undefined) {
         // Node/Express headers can be an array or a single value. We join