diff --git a/lib/linguist/blob_helper.rb b/lib/linguist/blob_helper.rb
index d7c70b4f..0cec2813 100644
--- a/lib/linguist/blob_helper.rb
+++ b/lib/linguist/blob_helper.rb
@@ -147,6 +147,7 @@ module Linguist
     # Return true or false
     def shebang_extname?
       extname.empty? &&
+        mode &&
         (mode.to_i(8) & 05) == 05
     end