diff --git a/src/mac/carbon/window.cpp b/src/mac/carbon/window.cpp
index 3cbaafa3c4..46f90f8732 100644
--- a/src/mac/carbon/window.cpp
+++ b/src/mac/carbon/window.cpp
@@ -507,7 +507,7 @@ pascal OSStatus wxMacUnicodeTextEventHandler( EventHandlerCallRef handler , Even
         numChars = dataSize / sizeof( UniChar) + 1;
         charBuf = buf ;
 
-        if ( numChars * 2 > sizeof(buf) )
+        if ( (size_t) numChars * 2 > sizeof(buf) )
             charBuf = new UniChar[ numChars ] ;
         else
             charBuf = buf ;