diff --git a/acme.sh b/acme.sh
index a9a9c04..dea5b4a 100755
--- a/acme.sh
+++ b/acme.sh
@@ -1716,6 +1716,7 @@ _send_signed_request() {
   while [ "${_request_retry_times}" -lt "$MAX_REQUEST_RETRY_TIMES" ]; do
     _debug3 _request_retry_times "$_request_retry_times"
     if [ -z "$_CACHED_NONCE" ]; then
+      _headers=""
       if [ "$ACME_NEW_NONCE" ]; then
         _debug2 "Get nonce. ACME_NEW_NONCE" "$ACME_NEW_NONCE"
         nonceurl="$ACME_NEW_NONCE"