diff --git a/xpcom/io/nsLocalFileWin.cpp b/xpcom/io/nsLocalFileWin.cpp
index afa055d9c5..5182b71f6f 100644
--- a/xpcom/io/nsLocalFileWin.cpp
+++ b/xpcom/io/nsLocalFileWin.cpp
@@ -3028,6 +3028,8 @@ nsLocalFile::IsExecutable(bool* aResult)
       "com",
       "cpl",
       "crt",
+      "der",
+      "diagcab",
       "exe",
       "fxp",         // FoxPro compiled app
       "hlp",