diff --git a/tests/test_utils_opmsg.py b/tests/test_utils_opmsg.py
index 3f4e58ebf..3b7093030 100644
--- a/tests/test_utils_opmsg.py
+++ b/tests/test_utils_opmsg.py
@@ -22,7 +22,7 @@ def ioc():
     STATUS_ENUMS   = ("OFFLINE", "PREPARATION", "REMOTE", "ATTENDED")
     CATEGORY_ENUMS = ("USER", "MD", "SD", "ACCESS", "DOWN")
 
-    def run_op_prefix(prefix: string):
+    def run_op_prefix(prefix: str):
         """
         OP message space:
           - STATUS (enum), STATUS-DATE (str)