diff --git a/packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.spec.ts b/packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.spec.ts
index bc742a907ac9..a3bf1337e2b2 100644
--- a/packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.spec.ts
+++ b/packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.spec.ts
@@ -23,7 +23,7 @@ describe("applyMd5BodyChecksumMiddleware", () => {
   });
 
   for (const body of ["body", new ArrayBuffer(10), new Uint8Array(10), void 0]) {
-    it("should calculate the body hash, encode the result, and set the encoded hash to Content-MD5 header", async () => {
+    it("should calculate the body hash, encode the result, and set the encoded hash to content-md5 header", async () => {
       const handler = applyMd5BodyChecksumMiddleware({
         md5: MockHash,
         base64Encoder: mockEncoder,
@@ -40,7 +40,7 @@ describe("applyMd5BodyChecksumMiddleware", () => {
 
       expect(next.mock.calls.length).toBe(1);
       const { request } = next.mock.calls[0][0];
-      expect(request.headers["Content-MD5"]).toBe("encoded");
+      expect(request.headers["content-md5"]).toBe("encoded");
       expect(mockHashUpdate.mock.calls).toEqual([[body || ""]]);
     });
 
@@ -65,7 +65,7 @@ describe("applyMd5BodyChecksumMiddleware", () => {
       expect(next.mock.calls.length).toBe(1);
       const { request } = next.mock.calls[0][0];
       expect(request.headers["CoNtEnT-Md5"]).toBe("foo");
-      expect(request.headers["Content-MD5"]).toBe(undefined);
+      expect(request.headers["content-md5"]).toBe(undefined);
       expect(mockHashUpdate.mock.calls.length).toBe(0);
       expect(mockHashDigest.mock.calls.length).toBe(0);
       expect(mockEncoder.mock.calls.length).toBe(0);
@@ -90,7 +90,7 @@ describe("applyMd5BodyChecksumMiddleware", () => {
     expect(next.mock.calls.length).toBe(1);
     const { request } = next.mock.calls[0][0];
     expect(request.body).toStrictEqual(new ExoticStream());
-    expect(request.headers["Content-MD5"]).toBe("encoded");
+    expect(request.headers["content-md5"]).toBe("encoded");
     expect(mockHashDigest.mock.calls.length).toBe(0);
     expect(mockEncoder.mock.calls.length).toBe(1);
     expect(mockEncoder.mock.calls).toEqual([[new Uint8Array(5)]]);
diff --git a/packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.ts b/packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.ts
index 430ef33c731a..23661c9dcd27 100644
--- a/packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.ts
+++ b/packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.ts
@@ -20,7 +20,7 @@ export const applyMd5BodyChecksumMiddleware =
     let { request } = args;
     if (HttpRequest.isInstance(request)) {
       const { body, headers } = request;
-      if (!hasHeader("Content-MD5", headers)) {
+      if (!hasHeader("content-md5", headers)) {
         let digest: Promise<Uint8Array>;
         if (body === undefined || typeof body === "string" || ArrayBuffer.isView(body) || isArrayBuffer(body)) {
           const hash = new options.md5();
@@ -34,7 +34,7 @@ export const applyMd5BodyChecksumMiddleware =
           ...request,
           headers: {
             ...headers,
-            "Content-MD5": options.base64Encoder(await digest),
+            "content-md5": options.base64Encoder(await digest),
           },
         };
       }