diff --git a/toolkit/system/gnome/nsAlertsIconListener.cpp b/toolkit/system/gnome/nsAlertsIconListener.cpp
index f0d06f734187..b967dedb7597 100644
--- a/toolkit/system/gnome/nsAlertsIconListener.cpp
+++ b/toolkit/system/gnome/nsAlertsIconListener.cpp
@@ -137,7 +137,9 @@ nsAlertsIconListener::OnLoadComplete(imgIRequest* aRequest)
 
   nsCOMPtr<imgIContainer> image;
   rv = aRequest->GetImage(getter_AddRefs(image));
-  MOZ_ASSERT(image);
+  if (NS_WARN_IF(NS_FAILED(rv) || !image)) {
+    return rv;
+  }
 
   // Ask the image to decode at its intrinsic size.
   int32_t width = 0, height = 0;