diff --git a/src/common/filename.cpp b/src/common/filename.cpp
index ae6440cc5a..7ca4edd295 100644
--- a/src/common/filename.cpp
+++ b/src/common/filename.cpp
@@ -1727,7 +1727,7 @@ public :
     m_type = from.m_type ;
     m_creator = from.m_creator ;
   }
-  MacDefaultExtensionRecord( char * extension , OSType type , OSType creator )
+  MacDefaultExtensionRecord( const char * extension , OSType type , OSType creator )
   {
     strncpy( m_ext , extension , kMacExtensionMaxLength ) ;
     m_ext[kMacExtensionMaxLength] = 0 ;