diff --git a/dom/apps/src/Webapps.js b/dom/apps/src/Webapps.js
index 69f0f199d137..98aaf4219a09 100644
--- a/dom/apps/src/Webapps.js
+++ b/dom/apps/src/Webapps.js
@@ -181,10 +181,17 @@ WebappsRegistry.prototype = {
 
   checkInstalled: function(aManifestURL) {
     let manifestURL = Services.io.newURI(aManifestURL, null, this._window.document.baseURIObject);
-    this._window.document.nodePrincipal.checkMayLoad(manifestURL, true, false);
 
     let request = this.createRequest();
 
+    try {
+      this._window.document.nodePrincipal.checkMayLoad(manifestURL, true,
+                                                       false);
+    } catch (ex) {
+      Services.DOMRequest.fireErrorAsync(request, "CROSS_ORIGIN_CHECK_NOT_ALLOWED");
+      return request;
+    }
+
     this.addMessageListeners("Webapps:CheckInstalled:Return:OK");
     cpmm.sendAsyncMessage("Webapps:CheckInstalled", { origin: this._getOrigin(this._window.location.href),
                                                       manifestURL: manifestURL.spec,
diff --git a/dom/tests/mochitest/webapps/file_bug_779982.html b/dom/tests/mochitest/webapps/file_bug_779982.html
index 12c7a0b6dbc5..4fe6d1a7c793 100644
--- a/dom/tests/mochitest/webapps/file_bug_779982.html
+++ b/dom/tests/mochitest/webapps/file_bug_779982.html
@@ -34,11 +34,16 @@
         break;
 
       case "checkInstalledWrong":
-        try {
-          navigator.mozApps.checkInstalled('http://something.org/manifest.webapp');
+        var request = navigator.mozApps.checkInstalled('http://something.org/manifest.webapp');
+        request.onsuccess = function() {
           finish(false);
-        } catch (e) {
-          finish(true);
+        }
+        request.onerror = function() {
+          if (this.error.name == "CROSS_ORIGIN_URL_NOT_ALLOWED") {
+            finish(true);
+          } else {
+            finish(false);
+          }
         }
         break;