diff --git a/toolkit/components/downloads/DownloadIntegration.jsm b/toolkit/components/downloads/DownloadIntegration.jsm
index 1649eb71ed3e..ba240f4d1ed2 100644
--- a/toolkit/components/downloads/DownloadIntegration.jsm
+++ b/toolkit/components/downloads/DownloadIntegration.jsm
@@ -595,7 +595,7 @@ var DownloadIntegration = {
     }
 
     let isWindowsExe = AppConstants.platform == "win" &&
-      fileExtension.toLowerCase() == "exe";
+      fileExtension && fileExtension.toLowerCase() == "exe";
 
     // Ask for confirmation if the file is executable, except for .exe on
     // Windows where the operating system will show the prompt based on the