diff --git a/strbuf.c b/strbuf.c
index 59678bf5b0..bad76ea64d 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -168,7 +168,7 @@ int strbuf_reencode(struct strbuf *sb, const char *from, const char *to)
 	if (!out)
 		return -1;
 
-	strbuf_attach(sb, out, len, len);
+	strbuf_attach(sb, out, len, len + 1);
 	return 0;
 }