diff --git a/packages/middleware-recursion-detection/src/index.spec.ts b/packages/middleware-recursion-detection/src/index.spec.ts
index 5b2452816021..8f5a81c2776d 100644
--- a/packages/middleware-recursion-detection/src/index.spec.ts
+++ b/packages/middleware-recursion-detection/src/index.spec.ts
@@ -70,6 +70,81 @@ 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 with some other casing`, 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: {
+          ["x-AmZn-TrAcE-iD"]: "some-real-trace-id",
+        },
+      }),
+    });
+
+    const { calls } = (mockNextHandler as any).mock;
+    expect(calls.length).toBe(1);
+    const { request } = mockNextHandler.mock.calls[0][0];
+    const existingTraceHeader = Object.keys(request.headers).find(
+      (h) => h.toLowerCase() === TRACE_ID_HEADER_NAME.toLowerCase()
+    );
+    expect(existingTraceHeader).toBeDefined();
+    expect(request.headers[existingTraceHeader!]).toBe("some-real-trace-id");
+  });
+
+  it(`should NOT set ${TRACE_ID_HEADER_NAME} header when the header is already set with alternating case`, 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: {
+          "X-aMzN-tRaCe-Id": "some-real-trace-id",
+        },
+      }),
+    });
+
+    const { calls } = (mockNextHandler as any).mock;
+    expect(calls.length).toBe(1);
+    const { request } = mockNextHandler.mock.calls[0][0];
+    const existingTraceHeader = Object.keys(request.headers).find(
+      (h) => h.toLowerCase() === TRACE_ID_HEADER_NAME.toLowerCase()
+    );
+    expect(existingTraceHeader).toBeDefined();
+    expect(request.headers[existingTraceHeader!]).toBe("some-real-trace-id");
+  });
+
+  it(`should NOT set ${TRACE_ID_HEADER_NAME} header when the header is already set with all uppercase`, 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: {
+          "X-AMZN-TRACE-ID": "some-real-trace-id",
+        },
+      }),
+    });
+
+    const { calls } = (mockNextHandler as any).mock;
+    expect(calls.length).toBe(1);
+    const { request } = mockNextHandler.mock.calls[0][0];
+    const existingTraceHeader = Object.keys(request.headers).find(
+      (h) => h.toLowerCase() === TRACE_ID_HEADER_NAME.toLowerCase()
+    );
+    expect(existingTraceHeader).toBeDefined();
+    expect(request.headers[existingTraceHeader!]).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..9030c34443c8 100644
--- a/packages/middleware-recursion-detection/src/index.ts
+++ b/packages/middleware-recursion-detection/src/index.ts
@@ -27,14 +27,16 @@ export const recursionDetectionMiddleware =
   <Output extends MetadataBearer>(next: BuildHandler<any, Output>): BuildHandler<any, Output> =>
   async (args: BuildHandlerArguments<any>): Promise<BuildHandlerOutput<Output>> => {
     const { request } = args;
-    if (
-      !HttpRequest.isInstance(request) ||
-      options.runtime !== "node" ||
-      request.headers.hasOwnProperty(TRACE_ID_HEADER_NAME)
-    ) {
+    if (!HttpRequest.isInstance(request) || options.runtime !== "node") {
       return next(args);
     }
+    const traceIdHeader =
+      Object.keys(request.headers ?? {}).find((h) => h.toLowerCase() === TRACE_ID_HEADER_NAME.toLowerCase()) ??
+      TRACE_ID_HEADER_NAME;
 
+    if (request.headers.hasOwnProperty(traceIdHeader)) {
+      return next(args);
+    }
     const functionName = process.env[ENV_LAMBDA_FUNCTION_NAME];
     const traceId = process.env[ENV_TRACE_ID];
     const nonEmptyString = (str: unknown): str is string => typeof str === "string" && str.length > 0;