diff --git a/common/rfb/PixelFormat.cxx b/common/rfb/PixelFormat.cxx
index 52e267a..185d437 100644
--- a/common/rfb/PixelFormat.cxx
+++ b/common/rfb/PixelFormat.cxx
@@ -205,6 +205,12 @@ bool PixelFormat::is888(void) const
     return false;
   if (blueMax != 255)
     return false;
+  if ((redShift & 0x7) != 0)
+    return false;
+  if ((greenShift & 0x7) != 0)
+    return false;
+  if ((blueShift & 0x7) != 0)
+    return false;
 
   return true;
 }