diff --git a/src/ert/config/parsing/lark_parser.py b/src/ert/config/parsing/lark_parser.py
index b1c62770645..f0076108aaf 100644
--- a/src/ert/config/parsing/lark_parser.py
+++ b/src/ert/config/parsing/lark_parser.py
@@ -263,7 +263,7 @@ def substitute_arg(
         raise ValueError(
             "Expected "
             "Union[FileContextToken, List[Tuple[FileContextToken]]], "
-            f"got {arg}"
+            f"got {type(arg)}"
         )
 
     return [