diff --git a/xrdp/xrdp_mm.c b/xrdp/xrdp_mm.c
index 260dea54..7fcb0120 100644
--- a/xrdp/xrdp_mm.c
+++ b/xrdp/xrdp_mm.c
@@ -2325,7 +2325,7 @@ xrdp_mm_frame_ack(struct xrdp_mm *self, int frame_id)
     }
     ex = self->wm->client_info->max_unacknowledged_frame_count;
     /* make sure we won't have too many in-flight frames */
-    if (self->encoder->frame_id_client + ex > self->encoder->frame_id_server)
+    if (self->encoder->frame_id_client + ex >= self->encoder->frame_id_server)
     {
         if (self->encoder->frame_id_server > self->encoder->frame_id_server_sent)
         {