diff --git a/src/thingdef/thingdef_states.cpp b/src/thingdef/thingdef_states.cpp
index bf48e671d..4df275921 100644
--- a/src/thingdef/thingdef_states.cpp
+++ b/src/thingdef/thingdef_states.cpp
@@ -583,7 +583,7 @@ FxVMFunctionCall *ParseAction(FScanner &sc, FState state, FString statestring, B
 		}
 		return call;
 	}
-	sc.ScriptError("Invalid state parameter %s\n", sc.String);
+	sc.ScriptError("Invalid parameter '%s'\n", sc.String);
 	return NULL;
 }