diff --git a/lib/doh.c b/lib/doh.c
index 988f35218..03e28beae 100644
--- a/lib/doh.c
+++ b/lib/doh.c
@@ -229,7 +229,7 @@ static CURLcode dohprobe(struct Curl_easy *data,
     ERROR_CHECK_SETOPT(CURLOPT_WRITEDATA, resp);
     if(!data->set.doh_get) {
       ERROR_CHECK_SETOPT(CURLOPT_POSTFIELDS, p->dohbuffer);
-      ERROR_CHECK_SETOPT(CURLOPT_POSTFIELDSIZE, p->dohlen);
+      ERROR_CHECK_SETOPT(CURLOPT_POSTFIELDSIZE, (long)p->dohlen);
     }
     ERROR_CHECK_SETOPT(CURLOPT_HTTPHEADER, headers);
     ERROR_CHECK_SETOPT(CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);