diff --git a/common/rfb/PixelFormat.cxx b/common/rfb/PixelFormat.cxx
index a9d015d..896f4e5 100644
--- a/common/rfb/PixelFormat.cxx
+++ b/common/rfb/PixelFormat.cxx
@@ -200,6 +200,12 @@ 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;
 }