diff --git a/lib/modules/datafile-manager/datafileManager.ts b/lib/modules/datafile-manager/datafileManager.ts
index abf11d8e9..5c9fdc6cd 100644
--- a/lib/modules/datafile-manager/datafileManager.ts
+++ b/lib/modules/datafile-manager/datafileManager.ts
@@ -44,6 +44,7 @@ export interface DatafileManagerConfig {
   updateInterval?: number;
   urlTemplate?: string;
   cache?: PersistentKeyValueCache;
+  customHeaders?: Record<string, string>;
 }
 
 export interface NodeDatafileManagerConfig extends DatafileManagerConfig {
diff --git a/lib/modules/datafile-manager/httpPollingDatafileManager.ts b/lib/modules/datafile-manager/httpPollingDatafileManager.ts
index c3311997e..c9b4ad2f4 100644
--- a/lib/modules/datafile-manager/httpPollingDatafileManager.ts
+++ b/lib/modules/datafile-manager/httpPollingDatafileManager.ts
@@ -15,7 +15,7 @@
  */
 
 import { getLogger } from '../logging';
-import { sprintf } from '../../utils/fns';
+import { sprintf, assign } from '../../utils/fns';
 import { DatafileManager, DatafileManagerConfig, DatafileUpdate } from './datafileManager';
 import EventEmitter, { Disposer } from './eventEmitter';
 import { AbortableRequest, Response, Headers } from './http';
@@ -96,6 +96,8 @@ export default abstract class HttpPollingDatafileManager implements DatafileMana
 
   private sdkKey: string;
 
+  private customHeaders?: Record<string, string>;
+
   // When true, this means the update interval timeout fired before the current
   // sync completed. In that case, we should sync again immediately upon
   // completion of the current request, instead of waiting another update
@@ -114,11 +116,13 @@ export default abstract class HttpPollingDatafileManager implements DatafileMana
       updateInterval = DEFAULT_UPDATE_INTERVAL,
       urlTemplate = DEFAULT_URL_TEMPLATE,
       cache = noOpKeyValueCache,
+      customHeaders,
     } = configWithDefaultsApplied;
 
     this.cache = cache;
     this.cacheKey = 'opt-datafile-' + sdkKey;
     this.sdkKey = sdkKey;
+    this.customHeaders = customHeaders;
     this.isReadyPromiseSettled = false;
     this.readyPromiseResolver = (): void => { };
     this.readyPromiseRejecter = (): void => { };
@@ -266,6 +270,11 @@ export default abstract class HttpPollingDatafileManager implements DatafileMana
 
   private syncDatafile(): void {
     const headers: Headers = {};
+    
+    if (this.customHeaders) {
+      assign(headers, this.customHeaders);
+    }
+    
     if (this.lastResponseLastModified) {
       headers['if-modified-since'] = this.lastResponseLastModified;
     }
diff --git a/lib/shared_types.ts b/lib/shared_types.ts
index 9e52c8a69..0dc03e41f 100644
--- a/lib/shared_types.ts
+++ b/lib/shared_types.ts
@@ -95,6 +95,7 @@ export interface DatafileOptions {
   updateInterval?: number;
   urlTemplate?: string;
   datafileAccessToken?: string;
+  customHeaders?: Record<string, string>;
 }
 
 export interface OdpOptions {
diff --git a/tests/nodeDatafileManager.spec.ts b/tests/nodeDatafileManager.spec.ts
index 14fb49d05..91c1363c3 100644
--- a/tests/nodeDatafileManager.spec.ts
+++ b/tests/nodeDatafileManager.spec.ts
@@ -183,4 +183,49 @@ describe('nodeDatafileManager', () => {
     expect(makeGetRequestSpy).toBeCalledWith('https://myawesomeurl/', expect.anything());
     await manager.stop();
   });
+
+  it('passes custom headers to makeGetRequest and merges with system headers', async () => {
+    makeGetRequestSpy.mockReturnValue({
+      abort: jest.fn(),
+      responsePromise: Promise.resolve({
+        statusCode: 200,
+        body: '{"foo":"bar"}',
+        headers: {
+          'last-modified': 'Fri, 08 Mar 2019 18:57:17 GMT',
+        },
+      }),
+    });
+    const manager = new NodeDatafileManager({
+      sdkKey: '1234',
+      autoUpdate: true,
+      customHeaders: {
+        'X-Custom-Header': 'custom-value',
+        'X-Environment': 'production',
+      },
+    });
+    manager.start();
+    await manager.onReady();
+    
+    // First request should have custom headers
+    expect(makeGetRequestSpy).toBeCalledTimes(1);
+    expect(makeGetRequestSpy.mock.calls[0][0]).toBe('https://cdn.optimizely.com/datafiles/1234.json');
+    expect(makeGetRequestSpy.mock.calls[0][1]).toEqual({
+      'X-Custom-Header': 'custom-value',
+      'X-Environment': 'production',
+    });
+    
+    // Advance time to trigger second request
+    await advanceTimersByTime(300000);
+    
+    // Second request should have both custom headers AND if-modified-since
+    expect(makeGetRequestSpy).toBeCalledTimes(2);
+    expect(makeGetRequestSpy.mock.calls[1][0]).toBe('https://cdn.optimizely.com/datafiles/1234.json');
+    expect(makeGetRequestSpy.mock.calls[1][1]).toEqual({
+      'X-Custom-Header': 'custom-value',
+      'X-Environment': 'production',
+      'if-modified-since': 'Fri, 08 Mar 2019 18:57:17 GMT',
+    });
+    
+    await manager.stop();
+  });
 });