diff --git a/source3/utils/ntlm_auth.c b/source3/utils/ntlm_auth.c
index ceb22e597f7..8ce453f4b92 100644
--- a/source3/utils/ntlm_auth.c
+++ b/source3/utils/ntlm_auth.c
@@ -576,10 +576,14 @@ NTSTATUS contact_winbind_auth_crap(const char *username,
 	memcpy(request.data.auth_crap.chal, challenge->data, MIN(challenge->length, 8));
 
 	if (lm_response && lm_response->length) {
+		size_t capped_lm_response_len = MIN(
+			lm_response->length,
+			sizeof(request.data.auth_crap.lm_resp));
+
 		memcpy(request.data.auth_crap.lm_resp,
 		       lm_response->data,
-		       MIN(lm_response->length, sizeof(request.data.auth_crap.lm_resp)));
-		request.data.auth_crap.lm_resp_len = lm_response->length;
+		       capped_lm_response_len);
+		request.data.auth_crap.lm_resp_len = capped_lm_response_len;
 	}
 
 	if (nt_response && nt_response->length) {