diff --git a/vncviewer/Viewport.cxx b/vncviewer/Viewport.cxx
index bb5c94e..2ce788f 100644
--- a/vncviewer/Viewport.cxx
+++ b/vncviewer/Viewport.cxx
@@ -373,6 +373,9 @@
   case XK_ISO_Level3_Shift:
     // FLTK tends to let this one leak through on X11...
     return XK_ISO_Level3_Shift;
+  case XK_Multi_key:
+    // Same for this...
+    return XK_Multi_key;
   }
 
   // Ctrl and Cmd tend to fudge input handling, so we need to cheat here