diff -r cc75c76972ee -r c0432d11811c src/gui/image/qpixmap_x11.cpp
--- a/src/gui/image/qpixmap_x11.cpp	Wed Apr 21 12:15:23 2010 +0300
+++ b/src/gui/image/qpixmap_x11.cpp	Wed Apr 21 20:15:53 2010 +0300
@@ -383,7 +383,7 @@
             return has;
         // Will implicitly also check format and return quickly for opaque types...
         checked = true;
-        has = const_cast<QImage *>(image)->data_ptr()->checkForAlphaPixels();
+        has = image->isNull() ? false : const_cast<QImage *>(image)->data_ptr()->checkForAlphaPixels();
         return has;
     }