diff --git a/src/typval.c b/src/typval.c
index b9f8f1c..db439cb 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -1305,6 +1305,7 @@
     {
 	typval_T tmp;
 
+	init_tv(&tmp);
 	f_string(varp, &tmp);
 	tv_get_string_buf(&tmp, buf);
 	clear_tv(varp);