1 files changed, 1 insertions, 1 deletions
diff --git a/string.c b/string.c
index f6797648b4..7fd09d0b3a 100644
--- a/string.c
+++ b/string.c
@@ -1448,7 +1448,7 @@ rb_str_cat(VALUE str, const char *ptr, long len)
     if (STR_ASSOC_P(str)) {
 	rb_str_modify(str);
 	if (STR_EMBED_P(str)) str_make_independent(str);
-	REALLOC_N(RSTRING(str)->as.heap.ptr, char, RSTRING(str)->as.heap.len+len);
+	REALLOC_N(RSTRING(str)->as.heap.ptr, char, RSTRING(str)->as.heap.len+len+1);
 	memcpy(RSTRING(str)->as.heap.ptr + RSTRING(str)->as.heap.len, ptr, len);
 	RSTRING(str)->as.heap.len += len;
 	RSTRING(str)->as.heap.ptr[RSTRING(str)->as.heap.len] = '\0'; /* sentinel */