diff --git a/Lib/ctypes/test/__init__.py b/Lib/ctypes/test/__init__.py
index e2878f2..70d647b 100644
--- a/Lib/ctypes/test/__init__.py
+++ b/Lib/ctypes/test/__init__.py
@@ -178,7 +178,7 @@
         elif flag == "-u":
             use_resources.extend(value.split(","))
         elif flag == "-x":
-            exclude.append(value.split(","))
+            exclude.extend(value.split(","))
 
     mask = "test_*.py"
     if args: