diff --git a/src/osx/utils_osx.cpp b/src/osx/utils_osx.cpp
index bfcf65f57c..d356a5c953 100644
--- a/src/osx/utils_osx.cpp
+++ b/src/osx/utils_osx.cpp
@@ -274,7 +274,7 @@ CGColorRef wxMacCreateCGColorFromHITheme( ThemeBrush brush )
 void wxMacStringToPascal( const wxString&from , unsigned char * to )
 {
     wxCharBuffer buf = from.mb_str( wxConvLocal );
-    int len = strlen(buf);
+    size_t len = buf.length();
 
     if ( len > 255 )
         len = 255;