diff --git a/modules/@angular/http/src/headers.ts b/modules/@angular/http/src/headers.ts
index 9d1f5982a8..553fb34f86 100644
--- a/modules/@angular/http/src/headers.ts
+++ b/modules/@angular/http/src/headers.ts
@@ -46,7 +46,7 @@ export class Headers {
   _headersMap: Map<string, string[]>;
   constructor(headers?: Headers|{[key: string]: any}) {
     if (headers instanceof Headers) {
-      this._headersMap = (<Headers>headers)._headersMap;
+      this._headersMap = new Map<string, string[]>((<Headers>headers)._headersMap);
       return;
     }
 
diff --git a/modules/@angular/http/test/headers_spec.ts b/modules/@angular/http/test/headers_spec.ts
index 9b79275ee2..ae8593a1ef 100644
--- a/modules/@angular/http/test/headers_spec.ts
+++ b/modules/@angular/http/test/headers_spec.ts
@@ -42,6 +42,14 @@ export function main() {
         expect(headers.get('foo')).toBe('bar');
         expect(headers.getAll('foo')).toEqual(['bar']);
       });
+      it('should not alter the values of a provided header template', () => {
+        // Spec at https://fetch.spec.whatwg.org/#concept-headers-fill
+        // test for https://github.com/angular/angular/issues/6845
+        const firstHeaders = new Headers();
+        const secondHeaders = new Headers(firstHeaders);
+        secondHeaders.append('Content-Type', 'image/jpeg');
+        expect(firstHeaders.has('Content-Type')).toBeFalsy();
+      });
     });