diff --git a/mozilla/layout/base/nsCSSFrameConstructor.cpp b/mozilla/layout/base/nsCSSFrameConstructor.cpp
index c5e64c06fb7..d08a3481c99 100644
--- a/mozilla/layout/base/nsCSSFrameConstructor.cpp
+++ b/mozilla/layout/base/nsCSSFrameConstructor.cpp
@@ -4533,7 +4533,7 @@ nsCSSFrameConstructor::GetFrameFor(nsIPresShell*    aPresShell,
       nsIComboboxControlFrame * comboboxFrame;
       res = frame->QueryInterface(nsCOMTypeInfo<nsIComboboxControlFrame>::GetIID(),
                                                (void**)&comboboxFrame);
-      if (comboboxFrame) {
+      if (NS_SUCCEEDED(res) && comboboxFrame) {
         nsIFrame * listFrame;
         comboboxFrame->GetDropDown(&listFrame);
         if (nsnull != listFrame) {
diff --git a/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp b/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp
index c5e64c06fb7..d08a3481c99 100644
--- a/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp
+++ b/mozilla/layout/html/style/src/nsCSSFrameConstructor.cpp
@@ -4533,7 +4533,7 @@ nsCSSFrameConstructor::GetFrameFor(nsIPresShell*    aPresShell,
       nsIComboboxControlFrame * comboboxFrame;
       res = frame->QueryInterface(nsCOMTypeInfo<nsIComboboxControlFrame>::GetIID(),
                                                (void**)&comboboxFrame);
-      if (comboboxFrame) {
+      if (NS_SUCCEEDED(res) && comboboxFrame) {
         nsIFrame * listFrame;
         comboboxFrame->GetDropDown(&listFrame);
         if (nsnull != listFrame) {