diff --git a/src/mmg/helpers.cpp b/src/mmg/helpers.cpp
index 69d9302da..efb2bbf7b 100644
--- a/src/mmg/helpers.cpp
+++ b/src/mmg/helpers.cpp
@@ -266,7 +266,7 @@ format_date_time(time_t date_time) {
 #if defined(SYS_WINDOWS)
 wxString
 format_tooltip(const wxString &s) {
-  return format_paragraph(s.c_str(), 0, L"", L"", 80);
+  return format_paragraph(static_cast<const wchar_t *>(s.wc_str()), 0, L"", L"", 80);
 }
 #endif