diff --git a/lib/curl_rtmp.c b/lib/curl_rtmp.c
index 2d7ce5ed2..97430647b 100644
--- a/lib/curl_rtmp.c
+++ b/lib/curl_rtmp.c
@@ -206,7 +206,7 @@ static CURLcode rtmp_connect(struct connectdata *conn, bool *done)
   RTMP *r = conn->proto.generic;
   SET_RCVTIMEO(tv, 10);
 
-  r->m_sb.sb_socket = conn->sock[FIRSTSOCKET];
+  r->m_sb.sb_socket = (int)conn->sock[FIRSTSOCKET];
 
   /* We have to know if it's a write before we send the
    * connect request packet