diff --git a/win/vncviewer/DesktopWindow.cxx b/win/vncviewer/DesktopWindow.cxx
index 744149d..49b6c3f 100644
--- a/win/vncviewer/DesktopWindow.cxx
+++ b/win/vncviewer/DesktopWindow.cxx
@@ -75,7 +75,7 @@
   try {
     result = _this->processMessage(msg, wParam, lParam);
   } catch (rfb::UnsupportedPixelFormatException &e) {
-    MsgBox(0, e.str(), MB_OK | MB_ICONINFORMATION);
+    MsgBox(0, (TCHAR *) e.str(), MB_OK | MB_ICONINFORMATION);
     _this->getCallback()->closeWindow();
   } catch (rdr::Exception& e) {
     vlog.error("untrapped: %s", e.str());