diff --git a/dom/cache/test/mochitest/test_cache_put.js b/dom/cache/test/mochitest/test_cache_put.js
index 8d76930473a..29e1b4bd5c4 100644
--- a/dom/cache/test/mochitest/test_cache_put.js
+++ b/dom/cache/test/mochitest/test_cache_put.js
@@ -15,10 +15,34 @@ Promise.all([fetch(url),
   return Promise.all([fetchResponse.text(),
                       response.text()]);
 }).then(function(results) {
-  // suppress large assert spam unless its relevent
+  // suppress large assert spam unless it's relevent
   if (results[0] !== results[1]) {
     is(results[0], results[1], 'stored response body should match original');
   }
+
+  // Now, try to overwrite the request with a different response object.
+  return cache.put(url, new Response("overwritten"));
+}).then(function() {
+  return cache.matchAll(url);
+}).then(function(result) {
+  is(result.length, 1, "Only one entry should exist");
+  return result[0].text();
+}).then(function(body) {
+  is(body, "overwritten", "The cache entry should be successfully overwritten");
+
+  // Now, try to write a URL with a fragment
+  return cache.put(url + "#fragment", new Response("more overwritten"));
+}).then(function() {
+  return cache.matchAll(url + "#differentFragment");
+}).then(function(result) {
+  is(result.length, 1, "Only one entry should exist");
+  return result[0].text();
+}).then(function(body) {
+  is(body, "more overwritten", "The cache entry should be successfully overwritten");
+
+  // TODO: Verify that trying to store a response with an error raises a TypeError
+  // when bug 1147178 is fixed.
+
   return caches.delete('putter' + context);
 }).then(function(deleted) {
   ok(deleted, "The cache should be deleted successfully");