diff --git a/ui/vnc.c b/ui/vnc.c
index 0fe6eff1b8..8bca59798c 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -2026,6 +2026,16 @@ static void set_pixel_format(VncState *vs,
         return;
     }
 
+    switch (bits_per_pixel) {
+    case 8:
+    case 16:
+    case 32:
+        break;
+    default:
+        vnc_client_error(vs);
+        return;
+    }
+
     vs->client_pf.rmax = red_max;
     vs->client_pf.rbits = hweight_long(red_max);
     vs->client_pf.rshift = red_shift;