diff --git a/src/gtk/utilsgtk.cpp b/src/gtk/utilsgtk.cpp
index 6b3e1751a2..e311c5fee2 100644
--- a/src/gtk/utilsgtk.cpp
+++ b/src/gtk/utilsgtk.cpp
@@ -192,11 +192,11 @@ wxCharBuffer wxConvertToGTK(const wxString& s, wxFontEncoding enc)
     wxWCharBuffer wbuf;
     if ( enc == wxFONTENCODING_SYSTEM || enc == wxFONTENCODING_DEFAULT )
     {
-        wbuf = wxConvUI->cMB2WC(s);
+        wbuf = wxConvUI->cMB2WC(s.c_str());
     }
     else // another encoding, use generic conversion class
     {
-        wbuf = wxCSConv(enc).cMB2WC(s);
+        wbuf = wxCSConv(enc).cMB2WC(s.c_str());
     }
 
     if ( !wbuf && !s.empty() )
@@ -207,7 +207,7 @@ wxCharBuffer wxConvertToGTK(const wxString& s, wxFontEncoding enc)
         // we choose ISO8859-1 here arbitrarily, it's just the most common
         // encoding probably and, also importantly here, conversion from it
         // never fails as it's done internally by wxCSConv
-        wbuf = wxCSConv(wxFONTENCODING_ISO8859_1).cMB2WC(s);
+        wbuf = wxCSConv(wxFONTENCODING_ISO8859_1).cMB2WC(s.c_str());
     }
 
     return wxConvUTF8.cWC2MB(wbuf);
@@ -217,7 +217,7 @@ wxCharBuffer wxConvertFromGTK(const wxString& s, wxFontEncoding enc)
 {
     // this conversion should never fail as GTK+ always uses UTF-8 internally
     // so there are no complications here
-    const wxWCharBuffer wbuf(wxConvUTF8.cMB2WC(s));
+    const wxWCharBuffer wbuf(wxConvUTF8.cMB2WC(s.c_str()));
     if ( enc == wxFONTENCODING_SYSTEM )
         return wxConvUI->cWC2MB(wbuf);