diff --git a/docs/latex/wx/wxstring.tex b/docs/latex/wx/wxstring.tex
index 445d0058f7..544bd55821 100644
--- a/docs/latex/wx/wxstring.tex
+++ b/docs/latex/wx/wxstring.tex
@@ -586,7 +586,7 @@ to a function expecting non-const pointer.
 
 \membersection{wxString::char\_str}\label{wxstringcharstr}
 
-\constfunc{wxWritableCharBuffer}{char\_str}{\void}
+\constfunc{wxWritableCharBuffer}{char\_str}{\param{wxMBConv\&}{ conv = wxConvLibc}}
 
 Returns an object with string data that is implicitly convertible to
 {\tt char*} pointer. Note that any change to the returned buffer is lost and so
diff --git a/include/wx/string.h b/include/wx/string.h
index d60073694c..c24ca6c5b5 100644
--- a/include/wx/string.h
+++ b/include/wx/string.h
@@ -1094,7 +1094,8 @@ public:
     // conversion to *non-const* multibyte or widestring buffer; modifying
     // returned buffer won't affect the string, these methods are only useful
     // for passing values to const-incorrect functions
-    wxWritableCharBuffer char_str() const { return mb_str(); }
+    wxWritableCharBuffer char_str(const wxMBConv& conv = wxConvLibc) const
+        { return mb_str(conv); }
     wxWritableWCharBuffer wchar_str() const { return wc_str(); }
 
     // conversion to/from plain (i.e. 7 bit) ASCII: this is useful for