diff --git a/src/diff.c b/src/diff.c
index 59dc658..a47259e 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -3294,7 +3294,7 @@
     int			col;
 
     if (in_vim9script()
-	    && (check_for_string_or_number_arg(argvars,0) == FAIL
+	    && (check_for_lnum_arg(argvars,0) == FAIL
 		|| check_for_number_arg(argvars, 1) == FAIL))
 	return;