diff --git a/include/wx/datstrm.h b/include/wx/datstrm.h
index c11de7b204..d83aa66993 100644
--- a/include/wx/datstrm.h
+++ b/include/wx/datstrm.h
@@ -22,7 +22,7 @@ class WXDLLIMPEXP_BASE wxDataInputStream
 {
 public:
 #if wxUSE_UNICODE
-    wxDataInputStream(wxInputStream& s, const wxMBConv& conv = wxConvAuto());
+    wxDataInputStream(wxInputStream& s, const wxMBConv& conv = wxConvUTF8 );
 #else
     wxDataInputStream(wxInputStream& s);
 #endif
@@ -98,7 +98,7 @@ class WXDLLIMPEXP_BASE wxDataOutputStream
 {
 public:
 #if wxUSE_UNICODE
-    wxDataOutputStream(wxOutputStream& s, const wxMBConv& conv = wxConvAuto());
+    wxDataOutputStream(wxOutputStream& s, const wxMBConv& conv = wxConvUTF8 );
 #else
     wxDataOutputStream(wxOutputStream& s);
 #endif
diff --git a/interface/wx/datstrm.h b/interface/wx/datstrm.h
index 387cb43467..8c7c72cdc6 100644
--- a/interface/wx/datstrm.h
+++ b/interface/wx/datstrm.h
@@ -43,7 +43,7 @@ public:
             instance! It is recommended to use the default value (UTF-8).
     */
     wxDataOutputStream(wxOutputStream& stream,
-                       const wxMBConv& conv = wxConvAuto());
+                       const wxMBConv& conv = wxConvUTF8);
 
     /**
         Destroys the wxDataOutputStream object.
@@ -190,7 +190,7 @@ public:
             instance!
     */
     wxDataInputStream(wxInputStream& stream,
-                      const wxMBConv& conv = wxConvAuto());
+                      const wxMBConv& conv = wxConvUTF8 );
 
     /**
         Destroys the wxDataInputStream object.