diff --git a/sds.c b/sds.c
index 49d2096..9d46dc4 100644
--- a/sds.c
+++ b/sds.c
@@ -513,7 +513,7 @@ sds sdscatvprintf(sds s, const char *fmt, va_list ap) {
     } else {
         buflen = sizeof(staticbuf);
     }
-
+    memset(buf, 0, buflen);
     /* Try with buffers two times bigger every time we fail to
      * fit the string in the current buffer size. */
     while(1) {