diff --git a/tests/test_utils_opmsg.py b/tests/test_utils_opmsg.py
index b77151ccf..a0c529c5f 100644
--- a/tests/test_utils_opmsg.py
+++ b/tests/test_utils_opmsg.py
@@ -39,7 +39,7 @@ def ioc():
                 "STATUS-DATE": str,
                 **{f"OP-DATE{i}": str for i in range(N_MSG_HISTORY)},
                 **{f"OP-MSG{i}": str for i in range(N_MSG_HISTORY)},
-                "OP-MSG-TMP": str,
+                **{"OP-MSG-TMP": ""},
             }
             mor.host(**pvdb)