diff --git a/src/errors.h b/src/errors.h
index 90aa292..965187f 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3306,3 +3306,7 @@
 EXTERN char e_invalid_argument_nr[]
 	INIT(= N_("E1291: Invalid argument: %ld"));
 #endif
+#ifdef FEAT_CMDWIN
+EXTERN char e_cmdline_window_already_open[]
+	INIT(= N_("E1292: Command-line window is already open"));
+#endif