diff --git a/src/qt/checkbox.cpp b/src/qt/checkbox.cpp
index 537daa4281..5196b684bd 100644
--- a/src/qt/checkbox.cpp
+++ b/src/qt/checkbox.cpp
@@ -119,6 +119,9 @@ wxCheckBoxState wxCheckBox::DoGet3StateValue() const
     case Qt::PartiallyChecked:
         return wxCHK_UNDETERMINED;
     }
+
+    wxFAIL_MSG( "unknown QCheckBox state" );
+    return wxCHK_UNDETERMINED;
 }
 
 QCheckBox *wxCheckBox::GetHandle() const