diff --git a/src/eval.c b/src/eval.c
index 7708796..2256589 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -26439,9 +26439,11 @@
     {
 	/* vim_strsave_shellescape() needs a NUL terminated string. */
 	c = (*fnamep)[*fnamelen];
-	(*fnamep)[*fnamelen] = NUL;
+	if (c != NUL)
+	    (*fnamep)[*fnamelen] = NUL;
 	p = vim_strsave_shellescape(*fnamep, FALSE, FALSE);
-	(*fnamep)[*fnamelen] = c;
+	if (c != NUL)
+	    (*fnamep)[*fnamelen] = c;
 	if (p == NULL)
 	    return -1;
 	vim_free(*bufp);