diff --git a/docshell/test/chrome/bug311007_window.xul b/docshell/test/chrome/bug311007_window.xul
index fd2cb7af5f34..730580cc2bd3 100644
--- a/docshell/test/chrome/bug311007_window.xul
+++ b/docshell/test/chrome/bug311007_window.xul
@@ -20,6 +20,11 @@
    Bug 307027
      "Going back from secure page to error page does not clear yellow bar"
 
+    And enhancements:
+
+    Bug 478927
+      onLocationChange should notify whether or not loading an error page.
+
  */
 
 const kDNSErrorURI = "https://example/err.html";
@@ -85,6 +90,10 @@ function step1B(aWebProgress, aRequest, aLocation, aFlags) {
                           .LOCATION_CHANGE_SAME_DOCUMENT),
      "DocShell loaded a document (1)");
 
+  ok((aFlags & Components.interfaces.nsIWebProgressListener
+                         .LOCATION_CHANGE_ERROR_PAGE),
+     "This page is an error page.");
+
   ok(!(aWebProgress.QueryInterface(Components.interfaces.nsIDocShell)
                    .securityUI.state &
        Components.interfaces.nsIWebProgressListener.STATE_IS_SECURE),
@@ -110,6 +119,10 @@ function step2B(aWebProgress, aRequest, aLocation, aFlags) {
                           .LOCATION_CHANGE_SAME_DOCUMENT),
      "DocShell loaded a document (2)");
 
+  ok(!(aFlags & Components.interfaces.nsIWebProgressListener
+                          .LOCATION_CHANGE_ERROR_PAGE),
+     "This page is not an error page.");
+
   ok((aWebProgress.QueryInterface(Components.interfaces.nsIDocShell)
                   .securityUI.state &
       Components.interfaces.nsIWebProgressListener.STATE_IS_SECURE),
@@ -136,6 +149,10 @@ function step3B(aWebProgress, aRequest, aLocation, aFlags) {
                          .LOCATION_CHANGE_SAME_DOCUMENT),
      "We are in the same document as before (3)");
 
+  ok(!(aFlags & Components.interfaces.nsIWebProgressListener
+                          .LOCATION_CHANGE_ERROR_PAGE),
+     "This page is not an error page.");
+
   ok((aWebProgress.QueryInterface(Components.interfaces.nsIDocShell)
                   .securityUI.state &
       Components.interfaces.nsIWebProgressListener.STATE_IS_SECURE),
@@ -162,6 +179,10 @@ function step4B(aWebProgress, aRequest, aLocation, aFlags) {
                           .LOCATION_CHANGE_SAME_DOCUMENT),
        "DocShell loaded a document (4)");
 
+  ok((aFlags & Components.interfaces.nsIWebProgressListener
+                         .LOCATION_CHANGE_ERROR_PAGE),
+     "This page is an error page.");
+
   ok(!(aWebProgress.QueryInterface(Components.interfaces.nsIDocShell)
                    .securityUI.state &
        Components.interfaces.nsIWebProgressListener.STATE_IS_SECURE),