diff --git a/dlls/advapi32/advapi.c b/dlls/advapi32/advapi.c
index c1ab8f344f3..e00eddeece6 100644
--- a/dlls/advapi32/advapi.c
+++ b/dlls/advapi32/advapi.c
@@ -53,21 +53,26 @@ WINE_DEFAULT_DEBUG_CHANNEL(advapi);
 BOOL WINAPI
 GetUserNameA( LPSTR lpszName, LPDWORD lpSize )
 {
-  size_t len;
-  const char *name = wine_get_user_name();
+    WCHAR *buffer;
+    BOOL ret;
 
-  /* We need to include the null character when determining the size of the buffer. */
-  len = strlen(name) + 1;
-  if (len > *lpSize)
-  {
-    SetLastError(ERROR_MORE_DATA);
-    *lpSize = len;
-    return 0;
-  }
-
-  *lpSize = len;
-  strcpy(lpszName, name);
-  return 1;
+    if (!(buffer = HeapAlloc( GetProcessHeap(), 0, *lpSize * 2 * sizeof(WCHAR) )))
+    {
+        SetLastError( ERROR_NOT_ENOUGH_MEMORY );
+        return FALSE;
+    }
+    ret = GetUserNameW( buffer, *lpSize * 2 );
+    if (ret)
+    {
+        if (!(*lpSize = WideCharToMultiByte( CP_ACP, 0, buffer, -1, lpszName, *lpSize, NULL, NULL )))
+        {
+            *lpSize = WideCharToMultiByte( CP_ACP, 0, buffer, -1, NULL, 0, NULL, NULL );
+            SetLastError( ERROR_MORE_DATA );
+            ret = FALSE;
+        }
+    }
+    HeapFree( GetProcessHeap(), 0, buffer );
+    return ret;
 }
 
 /******************************************************************************
@@ -79,7 +84,7 @@ BOOL WINAPI
 GetUserNameW( LPWSTR lpszName, LPDWORD lpSize )
 {
     const char *name = wine_get_user_name();
-    DWORD len = MultiByteToWideChar( CP_ACP, 0, name, -1, NULL, 0 );
+    DWORD len = MultiByteToWideChar( CP_UNIXCP, 0, name, -1, NULL, 0 );
 
     if (len > *lpSize)
     {
@@ -89,7 +94,7 @@ GetUserNameW( LPWSTR lpszName, LPDWORD lpSize )
     }
 
     *lpSize = len;
-    MultiByteToWideChar( CP_ACP, 0, name, -1, lpszName, len );
+    MultiByteToWideChar( CP_UNIXCP, 0, name, -1, lpszName, len );
     return TRUE;
 }
 
diff --git a/dlls/ntdll/reg.c b/dlls/ntdll/reg.c
index b2131935875..7a4f593859f 100644
--- a/dlls/ntdll/reg.c
+++ b/dlls/ntdll/reg.c
@@ -728,20 +728,17 @@ NTSTATUS WINAPI NtUnloadKey(
  */
 NTSTATUS WINAPI RtlFormatCurrentUserKeyPath( IN OUT PUNICODE_STRING KeyPath)
 {
+    static const WCHAR pathW[] = {'\\','R','e','g','i','s','t','r','y','\\','U','s','e','r','\\'};
     const char *user = wine_get_user_name();
-    char *buffer;
-    ANSI_STRING AnsiPath;
-    NTSTATUS ret;
+    int len = ntdll_umbstowcs( 0, user, strlen(user)+1, NULL, 0 );
 
-    if (!(buffer = RtlAllocateHeap( GetProcessHeap(), 0, strlen(user)+16 )))
+    KeyPath->MaximumLength = sizeof(pathW) + len * sizeof(WCHAR);
+    KeyPath->Length = KeyPath->MaximumLength - sizeof(WCHAR);
+    if (!(KeyPath->Buffer = RtlAllocateHeap( GetProcessHeap(), 0, KeyPath->MaximumLength )))
         return STATUS_NO_MEMORY;
-
-    strcpy( buffer, "\\Registry\\User\\" );
-    strcat( buffer, user );
-    RtlInitAnsiString( &AnsiPath, buffer );
-    ret = RtlAnsiStringToUnicodeString(KeyPath, &AnsiPath, TRUE);
-    RtlFreeAnsiString( &AnsiPath );
-    return ret;
+    memcpy( KeyPath->Buffer, pathW, sizeof(pathW) );
+    ntdll_umbstowcs( 0, user, strlen(user)+1, KeyPath->Buffer + sizeof(pathW)/sizeof(WCHAR), len );
+    return STATUS_SUCCESS;
 }
 
 /******************************************************************************
diff --git a/dlls/ntdll/sec.c b/dlls/ntdll/sec.c
index 57bcaf3db52..04cbf3bd9eb 100644
--- a/dlls/ntdll/sec.c
+++ b/dlls/ntdll/sec.c
@@ -1178,17 +1178,22 @@ NTSTATUS WINAPI RtlConvertSidToUnicodeString(
        PSID Sid,
        BOOLEAN AllocateString)
 {
-        const char *p = wine_get_user_name();
-        NTSTATUS status;
-        ANSI_STRING AnsiStr;
+    const char *user = wine_get_user_name();
+    int len = ntdll_umbstowcs( 0, user, strlen(user)+1, NULL, 0 ) * sizeof(WCHAR);
 
-	FIXME("(%p %p %u)\n", String, Sid, AllocateString);
+    FIXME("(%p %p %u)\n", String, Sid, AllocateString);
 
-        RtlInitAnsiString(&AnsiStr, p);
-        status = RtlAnsiStringToUnicodeString(String, &AnsiStr, AllocateString);
+    String->Length = len - sizeof(WCHAR);
+    if (AllocateString)
+    {
+        String->MaximumLength = len;
+        if (!(String->Buffer = RtlAllocateHeap( GetProcessHeap(), 0, len )))
+            return STATUS_NO_MEMORY;
+    }
+    else if (len > String->MaximumLength) return STATUS_BUFFER_OVERFLOW;
 
-        TRACE("%s (%u %u)\n",debugstr_w(String->Buffer),String->Length,String->MaximumLength);
-        return status;
+    ntdll_umbstowcs( 0, user, strlen(user)+1, String->Buffer, len/sizeof(WCHAR) );
+    return STATUS_SUCCESS;
 }
 
 /******************************************************************************