diff --git a/libmproxy/script.py b/libmproxy/script.py
index 6dd791996..8bfacb382 100644
--- a/libmproxy/script.py
+++ b/libmproxy/script.py
@@ -83,7 +83,7 @@ class Script:
                  "If your script path contains spaces, "
                  "make sure to wrap it in additional quotes, e.g. -s \"'./foo bar/baz.py' --args\".") %
                 args[0])
-        elif not os.path.isfile(args[0]):
+        elif os.path.isdir(args[0]):
             raise ScriptError("Not a file: %s" % args[0])
         return args