diff --git a/src/eval.c b/src/eval.c
index 990fa8c..9091f79 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -26439,6 +26439,8 @@
 
     if (src[*usedlen] == ':' && src[*usedlen + 1] == 'S')
     {
+	/* vim_strsave_shellescape() needs a NUL terminated string. */
+	(*fnamep)[*fnamelen] = NUL;
 	p = vim_strsave_shellescape(*fnamep, FALSE, FALSE);
 	if (p == NULL)
 	    return -1;