diff --git a/include/wx/motif/private.h b/include/wx/motif/private.h
index 36b0c038fe..4f87d491ee 100644
--- a/include/wx/motif/private.h
+++ b/include/wx/motif/private.h
@@ -139,8 +139,8 @@ public:
 
     wxXmString(const wxString& str)
     {
-        m_string = XmStringCreateLtoR((char *)str.c_str(),
-            XmSTRING_DEFAULT_CHARSET);
+        m_string = XmStringCreateLtoR((char *)str.mb_str(),
+                                      XmSTRING_DEFAULT_CHARSET);
     }
 
     // just to avoid calling XmStringFree()