1 files changed, 1 insertions, 0 deletions
diff --git a/string.c b/string.c
index 78620b8048..29e84e3ffe 100644
--- a/string.c
+++ b/string.c
@@ -1667,6 +1667,7 @@ rb_str_unlocktmp(VALUE str)
 void
 rb_str_set_len(VALUE str, long len)
 {
+    rb_str_modify(str);
     STR_SET_LEN(str, len);
     RSTRING_PTR(str)[len] = '\0';
 }