Index: lib/sdk/crt/printf/streamout.c
===================================================================
--- lib/sdk/crt/printf/streamout.c	(revision 51001)
+++ lib/sdk/crt/printf/streamout.c	(working copy)
@@ -262,14 +262,16 @@
     TCHAR chr;
     int written = 0;
 
-    while (count--)
+    while (count)
     {
 #ifdef _UNICODE
         int len;
-        if ((len = mbtowc(&chr, string, MB_CUR_MAX)) < 1) break;
+        if ((len = mbtowc(&chr, string, count)) < 1) break;
         string += len;
+        count -= len;
 #else
         chr = *string++;
+        --count;
 #endif
         if (streamout_char(stream, chr) == 0) return -1;
         written++;
Index: lib/sdk/crt/string/mbstowcs_nt.c
===================================================================
--- lib/sdk/crt/string/mbstowcs_nt.c	(revision 51001)
+++ lib/sdk/crt/string/mbstowcs_nt.c	(working copy)
@@ -4,26 +4,29 @@
 #include <ndk/rtlfuncs.h>
 #include <string.h>
 
+WCHAR NTAPI RtlAnsiCharToUnicodeChar(IN OUT PUCHAR *AnsiChar);
+#undef MB_CUR_MAX
+#define MB_CUR_MAX 2
+
 /*
  * @implemented
  */
 int mbtowc (wchar_t *wchar, const char *mbchar, size_t count)
 {
-	NTSTATUS Status;
-	ULONG Size;
+	UCHAR mbarr[MB_CUR_MAX] = { 0 };
+	PUCHAR mbs = mbarr;
 
+	if (mbchar == NULL)
+		return 0;
+
 	if (wchar == NULL)
 		return 0;
 
-	Status = RtlMultiByteToUnicodeN (wchar,
-	                                 sizeof(WCHAR),
-	                                 &Size,
-	                                 mbchar,
-	                                 count);
-	if (!NT_SUCCESS(Status))
-		return -1;
+	memcpy(mbarr, mbchar, min(count, sizeof mbarr));
 
-	return (int)Size;
+	*wchar = RtlAnsiCharToUnicodeChar(&mbs);
+
+	return mbs - mbarr;
 }
 
 /*