diff --git a/packages/middleware-recursion-detection/src/index.spec.ts b/packages/middleware-recursion-detection/src/index.spec.ts
index 5b2452816021..2d4aa06bab83 100644
--- a/packages/middleware-recursion-detection/src/index.spec.ts
+++ b/packages/middleware-recursion-detection/src/index.spec.ts
@@ -70,6 +70,27 @@ describe(recursionDetectionMiddleware.name, () => {
     expect(request.headers[TRACE_ID_HEADER_NAME]).toBe("some-real-trace-id");
   });
 
+  it(`should NOT set ${TRACE_ID_HEADER_NAME} header when the header is already set in all lowercase`, async () => {
+    process.env = {
+      AWS_LAMBDA_FUNCTION_NAME: "some-function",
+      _X_AMZN_TRACE_ID: "some-trace-id",
+    };
+    const handler = recursionDetectionMiddleware({ runtime: "node" })(mockNextHandler, {} as any);
+    await handler({
+      input: {},
+      request: new HttpRequest({
+        headers: {
+          [TRACE_ID_HEADER_NAME.toLowerCase()]: "some-real-trace-id",
+        },
+      }),
+    });
+
+    const { calls } = (mockNextHandler as any).mock;
+    expect(calls.length).toBe(1);
+    const { request } = mockNextHandler.mock.calls[0][0];
+    expect(request.headers[TRACE_ID_HEADER_NAME.toLowerCase()]).toBe("some-real-trace-id");
+  });
+
   it("has no effect for browser runtime", async () => {
     process.env = {
       AWS_LAMBDA_FUNCTION_NAME: "some-function",
diff --git a/packages/middleware-recursion-detection/src/index.ts b/packages/middleware-recursion-detection/src/index.ts
index 42fb46ecfdc9..1ac9e78f677e 100644
--- a/packages/middleware-recursion-detection/src/index.ts
+++ b/packages/middleware-recursion-detection/src/index.ts
@@ -30,7 +30,9 @@ export const recursionDetectionMiddleware =
     if (
       !HttpRequest.isInstance(request) ||
       options.runtime !== "node" ||
-      request.headers.hasOwnProperty(TRACE_ID_HEADER_NAME)
+      Object.keys(request.headers).some(
+        (key) => key.toLowerCase() === TRACE_ID_HEADER_NAME.toLowerCase()
+      )
     ) {
       return next(args);
     }