diff --git a/src/sign.c b/src/sign.c
index c208a0e..6d62afa 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -2301,7 +2301,7 @@
 	return;
 
     if (in_vim9script()
-	    && (check_for_opt_string_or_number_arg(argvars, 0) == FAIL
+	    && (check_for_opt_buffer_arg(argvars, 0) == FAIL
 		|| (argvars[0].v_type != VAR_UNKNOWN
 		    && check_for_opt_dict_arg(argvars, 1) == FAIL)))
 	return;