diff --git a/src/mutex.inl b/src/mutex.inl
index 3a279666..4a295633 100644
--- a/src/mutex.inl
+++ b/src/mutex.inl
@@ -61,8 +61,10 @@ inline void* new_critical_section()
 inline void* new_mutex(const char* name)
 {
 #if defined(BOOST_NO_ANSI_APIS)
-    USES_CONVERSION;
-    HANDLE mutex = CreateMutexW(0, 0, A2CW(name));
+    int num_wide_chars = (strlen(name) + 1);
+    LPWSTR wide_name = (LPWSTR)_alloca( num_wide_chars * 2 );
+    ::MultiByteToWideChar(CP_ACP, 0, name, -1, wide_name, num_wide_chars);
+    HANDLE mutex = CreateMutexW(0, 0, wide_name);
 #else
     HANDLE mutex = CreateMutexA(0, 0, name);
 #endif
diff --git a/src/once.cpp b/src/once.cpp
index bbbfae60..54820694 100644
--- a/src/once.cpp
+++ b/src/once.cpp
@@ -18,6 +18,7 @@
       using std::size_t;
 #   endif
 #   include <windows.h>
+#   include "mutex.inl"
 #   if defined(BOOST_NO_STRINGSTREAM)
 #       include <strstream>
 
@@ -137,11 +138,7 @@ void call_once(void (*func)(), once_flag& flag)
              << &flag 
              << std::ends;
         unfreezer unfreeze(strm);
-#   if defined (BOOST_NO_ANSI_APIS)
-        USES_CONVERSION;
-        HANDLE mutex = CreateMutexW(NULL, FALSE, A2CW(strm.str()));
-#   else
-        HANDLE mutex = CreateMutexA(NULL, FALSE, strm.str());
+        HANDLE mutex=new_mutex(strm.str());
 #   endif
 #else
 #   if defined (BOOST_NO_ANSI_APIS)