diff --git a/src/mac/carbon/dccg.cpp b/src/mac/carbon/dccg.cpp
index 4abd9a625c..1d6f223a2f 100755
--- a/src/mac/carbon/dccg.cpp
+++ b/src/mac/carbon/dccg.cpp
@@ -2033,7 +2033,7 @@ bool wxDC::DoBlit(
     }
     else
     {
-        wxFAIL_MSG( wxT("Blitting is only supported from bitmap contexts") ) ;
+        wxFAIL_MSG( wxT("Blitting is only supported from bitmap contexts, and only with wxCOPY logical operation.") ) ;
         return false ; 
     }