diff --git a/libc/Makefile b/libc/Makefile
index 1267515a..f7fce25e 100644
--- a/libc/Makefile
+++ b/libc/Makefile
@@ -78,6 +78,7 @@ ldiv.o \
 lldiv.o \
 localtime.o \
 localtime_r.o \
+mblen.o \
 mbrlen.o \
 mbrtowc.o \
 mbsrtowcs.o \
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index ba9e3b11..892cb12f 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -81,6 +81,7 @@ ldiv_t ldiv(long, long);
 long long llabs(long long);
 lldiv_t lldiv(long long, long long);
 void* malloc(size_t);
+int mblen(const char*, size_t);
 size_t mbstowcs(wchar_t* __restrict, const char* __restrict, size_t);
 int mbtowc(wchar_t *__restrict, const char* __restrict, size_t);
 #if !defined(_SORTIX_SOURCE)
@@ -132,7 +133,6 @@ long jrand48(unsigned short [3]);
 char* l64a(long);
 void lcong48(unsigned short [7]);
 long lrand48(void);
-int mblen(const char*, size_t);
 char* mkdtemp(char*);
 int mkstemp(char*);
 long mrand48(void);
diff --git a/libc/mblen.cpp b/libc/mblen.cpp
new file mode 100644
index 00000000..6cbf0ad9
--- /dev/null
+++ b/libc/mblen.cpp
@@ -0,0 +1,43 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or (at your
+    option) any later version.
+
+    The Sortix C Library is distributed in the hope that it will be useful, but
+    WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    mblen.cpp
+    Determine number of bytes in next multibyte character.
+
+*******************************************************************************/
+
+#include <stdlib.h>
+#include <string.h>
+#include <wchar.h>
+
+extern "C" int mblen(const char* s, size_t n)
+{
+	static mbstate_t ps;
+	if ( !s )
+	{
+		memset(&ps, 0, sizeof(ps));
+		return 0; // TODO: Give the correct return value depending on ps.
+	}
+	size_t ret = mbrlen(s, n, &ps);
+	if ( ret == (size_t) -2 )
+		return -1;
+	if ( ret == (size_t) -1 )
+		return -1;
+	return (int) ret;
+}