diff --git a/ui/vnc-enc-tight.c b/ui/vnc-enc-tight.c
index e6966aebc3..59b59c0c79 100644
--- a/ui/vnc-enc-tight.c
+++ b/ui/vnc-enc-tight.c
@@ -330,7 +330,7 @@ tight_detect_smooth_image(VncState *vs, int w, int h)
     } else {
         errors = tight_detect_smooth_image16(vs, w, h);
     }
-    if (quality != -1) {
+    if (quality != (uint8_t)-1) {
         return (errors < tight_conf[quality].jpeg_threshold);
     }
     return (errors < tight_conf[compression].gradient_threshold);