diff --git a/handwritten/storage/src/nodejs-common/util.ts b/handwritten/storage/src/nodejs-common/util.ts
index 34b37c30f6a0..e6c4db98b095 100644
--- a/handwritten/storage/src/nodejs-common/util.ts
+++ b/handwritten/storage/src/nodejs-common/util.ts
@@ -970,6 +970,24 @@ export class Util {
       delete reqOpts.json.autoPaginate;
       delete reqOpts.json.autoPaginateVal;
       reqOpts.json = replaceProjectIdToken(reqOpts.json, projectId);
+
+      const headers = reqOpts.headers || {};
+      if (
+        typeof (headers as any).set === 'function' &&
+        typeof (headers as any).has === 'function'
+      ) {
+        if (!(headers as any).has('content-type')) {
+          (headers as any).set('Content-Type', 'application/json');
+        }
+        reqOpts.headers = headers;
+      } else {
+        const hasContentType = Object.keys(headers).some(
+          key => key.toLowerCase() === 'content-type'
+        );
+        reqOpts.headers = hasContentType
+          ? headers
+          : { ...headers, 'Content-Type': 'application/json' };
+      }
     }
 
     reqOpts.uri = replaceProjectIdToken(reqOpts.uri, projectId);
diff --git a/handwritten/storage/test/nodejs-common/util.ts b/handwritten/storage/test/nodejs-common/util.ts
index 3efc73d11d6c..88e6905ffb52 100644
--- a/handwritten/storage/test/nodejs-common/util.ts
+++ b/handwritten/storage/test/nodejs-common/util.ts
@@ -1805,6 +1805,64 @@ describe('common/util', () => {
       assert.deepStrictEqual(decoratedRequest.json, decoratedJson);
     });
 
+    it('should set Content-Type header on plain headers object when json is set', () => {
+      const projectId = 'project-id';
+      const reqOpts = {
+        uri: 'http://',
+        json: {},
+        headers: {},
+      };
+      replaceProjectIdTokenOverride = (x: any) => x;
+
+      const decoratedRequest = util.decorateRequest(reqOpts, projectId);
+      assert.strictEqual(
+        (decoratedRequest.headers as any)['Content-Type'],
+        'application/json'
+      );
+    });
+
+    it('should set Content-Type header on Headers instance when json is set', () => {
+      if (typeof Headers === 'undefined') {
+        return;
+      }
+      const projectId = 'project-id';
+      const headersInstance = new Headers();
+      const reqOpts = {
+        uri: 'http://',
+        json: {},
+        headers: headersInstance,
+      };
+      replaceProjectIdTokenOverride = (x: any) => x;
+
+      const decoratedRequest = util.decorateRequest(reqOpts as any, projectId);
+      assert.strictEqual(
+        (decoratedRequest.headers as any).get('Content-Type'),
+        'application/json'
+      );
+    });
+
+    it('should not overwrite existing Content-Type header if already present', () => {
+      const projectId = 'project-id';
+      const reqOpts = {
+        uri: 'http://',
+        json: {},
+        headers: {
+          'content-type': 'application/x-protobuf',
+        },
+      };
+      replaceProjectIdTokenOverride = (x: any) => x;
+
+      const decoratedRequest = util.decorateRequest(reqOpts, projectId);
+      assert.strictEqual(
+        (decoratedRequest.headers as any)['content-type'],
+        'application/x-protobuf'
+      );
+      assert.strictEqual(
+        (decoratedRequest.headers as any)['Content-Type'],
+        undefined
+      );
+    });
+
     it('should decorate the request', () => {
       const projectId = 'project-id';
       const reqOpts = {