diff --git a/libc/Makefile b/libc/Makefile
index cf8a9620..f20d6828 100644
--- a/libc/Makefile
+++ b/libc/Makefile
@@ -91,6 +91,7 @@ stdio/flbf.o \
 stdio/flbf_unlocked.o \
 stdio/flockfile.o \
 stdio/flushlbf.o \
+stdio/fmemopen.o \
 stdio/fnewfile.o \
 stdio/fparsemode.o \
 stdio/fpending.o \
diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index 4c83b532..86fdbd26 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -119,6 +119,7 @@ int fgetpos(FILE* __restrict stream, fpos_t* __restrict pos);
 char* fgets(char* __restrict s, int n, FILE* __restrict stream);
 char* fgets_unlocked(char* __restrict, int, FILE* __restrict);
 void flockfile(FILE* file);
+FILE* fmemopen(void* __restrict, size_t, const char* __restrict);
 FILE* fopen(const char* __restrict filename, const char* __restrict mode);
 int fprintf(FILE* __restrict stream, const char* __restrict format, ...)
 	__attribute__((__format__ (printf, 2, 3)));
@@ -210,7 +211,6 @@ int vsscanf(const char* __restrict s, const char* __restrict format, __gnuc_va_l
 /* TODO: These are not implemented in sortix libc yet. */
 #if 0
 char* ctermid(char* s);
-FILE *fmemopen(void* __restrict buf, size_t size, const char* __restrict mode);
 FILE* open_memstream(char** bufp, size_t* sizep);
 #endif
 
diff --git a/libc/stdio/fmemopen.cpp b/libc/stdio/fmemopen.cpp
new file mode 100644
index 00000000..066c7015
--- /dev/null
+++ b/libc/stdio/fmemopen.cpp
@@ -0,0 +1,224 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2014.
+
+    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/>.
+
+    libc/stdio/fmemopen.cpp
+    Open a memory buffer stream.
+
+*******************************************************************************/
+
+#include <sys/types.h>
+
+#include <errno.h>
+#include <FILE.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static const int FMEMOPEN_ALLOCATED = 1 << 0;
+
+struct fmemopen_state
+{
+	unsigned char* buffer;
+	size_t buffer_true_size;
+	size_t buffer_size;
+	size_t buffer_offset;
+	size_t buffer_used;
+	int flags;
+	int mode;
+};
+
+static ssize_t fmemopen_read(void* state_ptr, void* dst, size_t count)
+{
+	struct fmemopen_state* state = (struct fmemopen_state*) state_ptr;
+
+	if ( !(state->mode & FILE_MODE_READ) )
+		return errno = EBADF, -1;
+
+	if ( (size_t) SSIZE_MAX < count )
+		count = SSIZE_MAX;
+
+	if ( state->buffer_used < state->buffer_offset )
+		return 0;
+
+	size_t available = state->buffer_used - state->buffer_offset;
+	if ( available < count )
+		count = available;
+
+	memcpy(dst, state->buffer + state->buffer_offset, count);
+	state->buffer_offset += count;
+
+	return count;
+}
+
+static ssize_t fmemopen_write(void* state_ptr, const void* src, size_t count)
+{
+	struct fmemopen_state* state = (struct fmemopen_state*) state_ptr;
+
+	if ( !(state->mode & FILE_MODE_WRITE) )
+		return errno = EBADF, -1;
+
+	if ( (size_t) SSIZE_MAX < count )
+		count = SSIZE_MAX;
+
+	if ( state->mode & FILE_MODE_APPEND )
+		state->buffer_offset = state->buffer_used;
+
+	if ( state->buffer_used < state->buffer_offset )
+	{
+		size_t distance = state->buffer_offset - state->buffer_used;
+		memset(state->buffer + state->buffer_used, 0, distance);
+		state->buffer_used = state->buffer_offset;
+	}
+
+	size_t available = state->buffer_size - state->buffer_offset;
+	if ( available < count )
+		count = available;
+
+	memcpy(state->buffer + state->buffer_offset, src, count);
+	state->buffer_offset += count;
+
+	if ( state->buffer_used < state->buffer_offset )
+	{
+		state->buffer_used = state->buffer_offset;
+		if ( !(state->mode & FILE_MODE_BINARY) )
+		{
+			if ( state->buffer_used < state->buffer_true_size )
+				state->buffer[state->buffer_used] = '\0';
+		}
+	}
+
+	return count;
+}
+
+static off_t fmemopen_seek(void* state_ptr, off_t offset, int whence)
+{
+	struct fmemopen_state* state = (struct fmemopen_state*) state_ptr;
+	off_t base;
+	switch ( whence )
+	{
+	case SEEK_SET: base = 0; break;
+	case SEEK_CUR: base = (off_t) state->buffer_offset; break;
+	case SEEK_END: base = (off_t) state->buffer_used; break;
+	default: return errno = EINVAL, -1;
+	}
+	if ( offset < -base || base - (off_t) state->buffer_size < offset )
+		return errno = EOVERFLOW, -1;
+	return (off_t) (state->buffer_offset = (size_t) (base + offset));
+}
+
+static int fmemopen_close(void* state_ptr)
+{
+	struct fmemopen_state* state = (struct fmemopen_state*) state_ptr;
+
+	if ( state->flags & FMEMOPEN_ALLOCATED )
+		free(state->buffer);
+
+	return 0;
+}
+
+extern "C"
+FILE* fmemopen(void* restrict buffer_ptr,
+               size_t buffer_size,
+               const char* restrict mode_str)
+{
+	int flags = 0;
+	int mode = fparsemode(mode_str);
+	if ( mode < 0 )
+		return (FILE*) NULL;
+
+	if ( mode & ~(FILE_MODE_READ | FILE_MODE_WRITE | FILE_MODE_CREATE |
+	              FILE_MODE_BINARY | FILE_MODE_TRUNCATE | FILE_MODE_APPEND) )
+		return errno = EINVAL, (FILE*) NULL;
+
+#if OFF_MAX < SIZE_MAX
+	if ( (uintmax_t) OFF_MAX < (uintmax_t) buffer_size )
+		return errno = EOVERFLOW, (FILE*) NULL;
+#endif
+
+	if ( !(mode & FILE_MODE_BINARY) &&
+	      (mode & FILE_MODE_WRITE) &&
+	     !(mode & FILE_MODE_READ) &&
+	     buffer_size == 0 )
+		return errno = EINVAL, (FILE*) NULL;
+
+	void* allocated_buffer = NULL;
+	if ( !buffer_ptr )
+	{
+		if ( !(buffer_ptr = allocated_buffer = calloc(buffer_size, 1)) )
+			return (FILE*) NULL;
+		flags |= FMEMOPEN_ALLOCATED;
+	}
+
+	struct fmemopen_state* state =
+		(struct fmemopen_state*) malloc(sizeof(struct fmemopen_state));
+	if ( !state )
+		return free(allocated_buffer), (FILE*) NULL;
+
+	FILE* fp = fnewfile();
+	if ( !fp )
+		return free(state), free(allocated_buffer), (FILE*) NULL;
+
+	memset(state, 0, sizeof(*state));
+	state->flags = flags;
+	state->mode = mode;
+	state->buffer = (unsigned char*) buffer_ptr;
+	state->buffer_size = buffer_size;
+	state->buffer_true_size = buffer_size;
+
+	if ( !(mode & FILE_MODE_BINARY) &&
+	      (mode & FILE_MODE_WRITE) &&
+	     !(mode & FILE_MODE_READ) )
+		state->buffer_size = state->buffer_true_size - 1;
+
+	if ( (mode & FILE_MODE_APPEND) && !(mode & FILE_MODE_BINARY) )
+	{
+		state->buffer_offset = strnlen((const char*) state->buffer, state->buffer_size);
+		state->buffer_used = state->buffer_offset;
+	}
+	else if ( mode & FILE_MODE_TRUNCATE )
+	{
+		state->buffer_offset = 0;
+		state->buffer_used = 0;
+	}
+	else
+	{
+		state->buffer_offset = 0;
+		state->buffer_used = state->buffer_size;
+	}
+
+	if ( !(state->mode & FILE_MODE_BINARY) && (mode & FILE_MODE_WRITE) )
+	{
+		if ( state->buffer_used < state->buffer_true_size )
+			state->buffer[state->buffer_used] = '\0';
+	}
+
+	if ( mode & FILE_MODE_READ )
+		fp->flags |= _FILE_READABLE;
+	if ( mode & FILE_MODE_WRITE )
+		fp->flags |= _FILE_WRITABLE;
+
+	fp->user = state;
+	fp->read_func = fmemopen_read;
+	fp->write_func = fmemopen_write;
+	fp->seek_func = fmemopen_seek;
+	fp->close_func = fmemopen_close;
+
+	return fp;
+}