diff --git a/mercurial/mpatch.c b/mercurial/mpatch.c
--- a/mercurial/mpatch.c
+++ b/mercurial/mpatch.c
@@ -41,7 +41,7 @@ struct mpatch_flist {
 	struct mpatch_frag *base, *head, *tail;
 };
 
-static struct mpatch_flist *lalloc(ssize_t size)
+struct mpatch_flist *lalloc(ssize_t size)
 {
 	struct mpatch_flist *a = NULL;
 
@@ -63,7 +63,7 @@ static struct mpatch_flist *lalloc(ssize
 	return NULL;
 }
 
-static void mpatch_lfree(struct mpatch_flist *a)
+void mpatch_lfree(struct mpatch_flist *a)
 {
 	if (a) {
 		free(a->base);
@@ -202,7 +202,7 @@ static struct mpatch_flist *combine(stru
 }
 
 /* decode a binary patch into a hunk list */
-static struct mpatch_flist *mpatch_decode(const char *bin, ssize_t len)
+struct mpatch_flist *mpatch_decode(const char *bin, ssize_t len)
 {
 	struct mpatch_flist *l;
 	struct mpatch_frag *lt;
@@ -238,7 +238,7 @@ static struct mpatch_flist *mpatch_decod
 }
 
 /* calculate the size of resultant text */
-static ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l)
+ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l)
 {
 	ssize_t outlen = 0, last = 0;
 	struct mpatch_frag *f = l->head;
@@ -260,7 +260,7 @@ static ssize_t mpatch_calcsize(ssize_t l
 	return outlen;
 }
 
-static int mpatch_apply(char *buf, const char *orig, ssize_t len,
+int mpatch_apply(char *buf, const char *orig, ssize_t len,
 	struct mpatch_flist *l)
 {
 	struct mpatch_frag *f = l->head;
@@ -286,7 +286,7 @@ static int mpatch_apply(char *buf, const
 }
 
 /* recursively generate a patch of all bins between start and end */
-static struct mpatch_flist *mpatch_fold(PyObject *bins, ssize_t start,
+struct mpatch_flist *mpatch_fold(PyObject *bins, ssize_t start,
 	ssize_t end)
 {
 	ssize_t len, blen;
@@ -308,121 +308,3 @@ static struct mpatch_flist *mpatch_fold(
 		       mpatch_fold(bins, start + len, end));
 }
 
-static PyObject *
-patches(PyObject *self, PyObject *args)
-{
-	PyObject *text, *bins, *result;
-	struct mpatch_flist *patch;
-	const char *in;
-	char *out;
-	Py_ssize_t len, outlen, inlen;
-
-	if (!PyArg_ParseTuple(args, "OO:mpatch", &text, &bins))
-		return NULL;
-
-	len = PyList_Size(bins);
-	if (!len) {
-		/* nothing to do */
-		Py_INCREF(text);
-		return text;
-	}
-
-	if (PyObject_AsCharBuffer(text, &in, &inlen))
-		return NULL;
-
-	patch = mpatch_fold(bins, 0, len);
-	if (!patch)
-		return NULL;
-
-	outlen = mpatch_calcsize(inlen, patch);
-	if (outlen < 0) {
-		result = NULL;
-		goto cleanup;
-	}
-	result = PyBytes_FromStringAndSize(NULL, outlen);
-	if (!result) {
-		result = NULL;
-		goto cleanup;
-	}
-	out = PyBytes_AsString(result);
-	if (!mpatch_apply(out, in, inlen, patch)) {
-		Py_DECREF(result);
-		result = NULL;
-	}
-cleanup:
-	mpatch_lfree(patch);
-	return result;
-}
-
-/* calculate size of a patched file directly */
-static PyObject *
-patchedsize(PyObject *self, PyObject *args)
-{
-	long orig, start, end, len, outlen = 0, last = 0, pos = 0;
-	Py_ssize_t patchlen;
-	char *bin;
-
-	if (!PyArg_ParseTuple(args, "ls#", &orig, &bin, &patchlen))
-		return NULL;
-
-	while (pos >= 0 && pos < patchlen) {
-		start = getbe32(bin + pos);
-		end = getbe32(bin + pos + 4);
-		len = getbe32(bin + pos + 8);
-		if (start > end)
-			break; /* sanity check */
-		pos += 12 + len;
-		outlen += start - last;
-		last = end;
-		outlen += len;
-	}
-
-	if (pos != patchlen) {
-		if (!PyErr_Occurred())
-			PyErr_SetString(mpatch_Error, "patch cannot be decoded");
-		return NULL;
-	}
-
-	outlen += orig - last;
-	return Py_BuildValue("l", outlen);
-}
-
-static PyMethodDef methods[] = {
-	{"patches", patches, METH_VARARGS, "apply a series of patches\n"},
-	{"patchedsize", patchedsize, METH_VARARGS, "calculed patched size\n"},
-	{NULL, NULL}
-};
-
-#ifdef IS_PY3K
-static struct PyModuleDef mpatch_module = {
-	PyModuleDef_HEAD_INIT,
-	"mpatch",
-	mpatch_doc,
-	-1,
-	methods
-};
-
-PyMODINIT_FUNC PyInit_mpatch(void)
-{
-	PyObject *m;
-
-	m = PyModule_Create(&mpatch_module);
-	if (m == NULL)
-		return NULL;
-
-	mpatch_Error = PyErr_NewException("mercurial.mpatch.mpatchError",
-					  NULL, NULL);
-	Py_INCREF(mpatch_Error);
-	PyModule_AddObject(m, "mpatchError", mpatch_Error);
-
-	return m;
-}
-#else
-PyMODINIT_FUNC
-initmpatch(void)
-{
-	Py_InitModule3("mpatch", methods, mpatch_doc);
-	mpatch_Error = PyErr_NewException("mercurial.mpatch.mpatchError",
-					  NULL, NULL);
-}
-#endif
diff --git a/mercurial/mpatch.h b/mercurial/mpatch.h
new file mode 100644
--- /dev/null
+++ b/mercurial/mpatch.h
@@ -0,0 +1,20 @@
+#ifndef _HG_MPATCH_H_
+#define _HG_MPATCH_H_
+
+struct mpatch_frag {
+	int start, end, len;
+	const char *data;
+};
+
+struct mpatch_flist {
+	struct mpatch_frag *base, *head, *tail;
+};
+
+int mpatch_decode(const char *bin, ssize_t len, struct mpatch_flist** res);
+ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l);
+void mpatch_lfree(struct mpatch_flist *a);
+int mpatch_apply(char *buf, const char *orig, ssize_t len,
+	struct mpatch_flist *l);
+struct mpatch_flist *mpatch_fold(void *bins, ssize_t start, ssize_t end);
+
+#endif
diff --git a/mercurial/mpatch.c b/mercurial/mpatch_module.c
copy from mercurial/mpatch.c
copy to mercurial/mpatch_module.c
--- a/mercurial/mpatch.c
+++ b/mercurial/mpatch_module.c
@@ -28,286 +28,11 @@
 #include "util.h"
 #include "bitmanipulation.h"
 #include "compat.h"
+#include "mpatch.h"
 
 static char mpatch_doc[] = "Efficient binary patching.";
 static PyObject *mpatch_Error;
 
-struct mpatch_frag {
-	int start, end, len;
-	const char *data;
-};
-
-struct mpatch_flist {
-	struct mpatch_frag *base, *head, *tail;
-};
-
-static struct mpatch_flist *lalloc(ssize_t size)
-{
-	struct mpatch_flist *a = NULL;
-
-	if (size < 1)
-		size = 1;
-
-	a = (struct mpatch_flist *)malloc(sizeof(struct mpatch_flist));
-	if (a) {
-		a->base = (struct mpatch_frag *)malloc(sizeof(struct mpatch_frag) * size);
-		if (a->base) {
-			a->head = a->tail = a->base;
-			return a;
-		}
-		free(a);
-		a = NULL;
-	}
-	if (!PyErr_Occurred())
-		PyErr_NoMemory();
-	return NULL;
-}
-
-static void mpatch_lfree(struct mpatch_flist *a)
-{
-	if (a) {
-		free(a->base);
-		free(a);
-	}
-}
-
-static ssize_t lsize(struct mpatch_flist *a)
-{
-	return a->tail - a->head;
-}
-
-/* move hunks in source that are less cut to dest, compensating
-   for changes in offset. the last hunk may be split if necessary.
-*/
-static int gather(struct mpatch_flist *dest, struct mpatch_flist *src, int cut,
-	int offset)
-{
-	struct mpatch_frag *d = dest->tail, *s = src->head;
-	int postend, c, l;
-
-	while (s != src->tail) {
-		if (s->start + offset >= cut)
-			break; /* we've gone far enough */
-
-		postend = offset + s->start + s->len;
-		if (postend <= cut) {
-			/* save this hunk */
-			offset += s->start + s->len - s->end;
-			*d++ = *s++;
-		}
-		else {
-			/* break up this hunk */
-			c = cut - offset;
-			if (s->end < c)
-				c = s->end;
-			l = cut - offset - s->start;
-			if (s->len < l)
-				l = s->len;
-
-			offset += s->start + l - c;
-
-			d->start = s->start;
-			d->end = c;
-			d->len = l;
-			d->data = s->data;
-			d++;
-			s->start = c;
-			s->len = s->len - l;
-			s->data = s->data + l;
-
-			break;
-		}
-	}
-
-	dest->tail = d;
-	src->head = s;
-	return offset;
-}
-
-/* like gather, but with no output list */
-static int discard(struct mpatch_flist *src, int cut, int offset)
-{
-	struct mpatch_frag *s = src->head;
-	int postend, c, l;
-
-	while (s != src->tail) {
-		if (s->start + offset >= cut)
-			break;
-
-		postend = offset + s->start + s->len;
-		if (postend <= cut) {
-			offset += s->start + s->len - s->end;
-			s++;
-		}
-		else {
-			c = cut - offset;
-			if (s->end < c)
-				c = s->end;
-			l = cut - offset - s->start;
-			if (s->len < l)
-				l = s->len;
-
-			offset += s->start + l - c;
-			s->start = c;
-			s->len = s->len - l;
-			s->data = s->data + l;
-
-			break;
-		}
-	}
-
-	src->head = s;
-	return offset;
-}
-
-/* combine hunk lists a and b, while adjusting b for offset changes in a/
-   this deletes a and b and returns the resultant list. */
-static struct mpatch_flist *combine(struct mpatch_flist *a,
-	struct mpatch_flist *b)
-{
-	struct mpatch_flist *c = NULL;
-	struct mpatch_frag *bh, *ct;
-	int offset = 0, post;
-
-	if (a && b)
-		c = lalloc((lsize(a) + lsize(b)) * 2);
-
-	if (c) {
-
-		for (bh = b->head; bh != b->tail; bh++) {
-			/* save old hunks */
-			offset = gather(c, a, bh->start, offset);
-
-			/* discard replaced hunks */
-			post = discard(a, bh->end, offset);
-
-			/* insert new hunk */
-			ct = c->tail;
-			ct->start = bh->start - offset;
-			ct->end = bh->end - post;
-			ct->len = bh->len;
-			ct->data = bh->data;
-			c->tail++;
-			offset = post;
-		}
-
-		/* hold on to tail from a */
-		memcpy(c->tail, a->head, sizeof(struct mpatch_frag) * lsize(a));
-		c->tail += lsize(a);
-	}
-
-	mpatch_lfree(a);
-	mpatch_lfree(b);
-	return c;
-}
-
-/* decode a binary patch into a hunk list */
-static struct mpatch_flist *mpatch_decode(const char *bin, ssize_t len)
-{
-	struct mpatch_flist *l;
-	struct mpatch_frag *lt;
-	int pos = 0;
-
-	/* assume worst case size, we won't have many of these lists */
-	l = lalloc(len / 12 + 1);
-	if (!l)
-		return NULL;
-
-	lt = l->tail;
-
-	while (pos >= 0 && pos < len) {
-		lt->start = getbe32(bin + pos);
-		lt->end = getbe32(bin + pos + 4);
-		lt->len = getbe32(bin + pos + 8);
-		lt->data = bin + pos + 12;
-		pos += 12 + lt->len;
-		if (lt->start > lt->end || lt->len < 0)
-			break; /* sanity check */
-		lt++;
-	}
-
-	if (pos != len) {
-		if (!PyErr_Occurred())
-			PyErr_SetString(mpatch_Error, "patch cannot be decoded");
-		mpatch_lfree(l);
-		return NULL;
-	}
-
-	l->tail = lt;
-	return l;
-}
-
-/* calculate the size of resultant text */
-static ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l)
-{
-	ssize_t outlen = 0, last = 0;
-	struct mpatch_frag *f = l->head;
-
-	while (f != l->tail) {
-		if (f->start < last || f->end > len) {
-			if (!PyErr_Occurred())
-				PyErr_SetString(mpatch_Error,
-				                "invalid patch");
-			return -1;
-		}
-		outlen += f->start - last;
-		last = f->end;
-		outlen += f->len;
-		f++;
-	}
-
-	outlen += len - last;
-	return outlen;
-}
-
-static int mpatch_apply(char *buf, const char *orig, ssize_t len,
-	struct mpatch_flist *l)
-{
-	struct mpatch_frag *f = l->head;
-	int last = 0;
-	char *p = buf;
-
-	while (f != l->tail) {
-		if (f->start < last || f->end > len) {
-			if (!PyErr_Occurred())
-				PyErr_SetString(mpatch_Error,
-				                "invalid patch");
-			return 0;
-		}
-		memcpy(p, orig + last, f->start - last);
-		p += f->start - last;
-		memcpy(p, f->data, f->len);
-		last = f->end;
-		p += f->len;
-		f++;
-	}
-	memcpy(p, orig + last, len - last);
-	return 1;
-}
-
-/* recursively generate a patch of all bins between start and end */
-static struct mpatch_flist *mpatch_fold(PyObject *bins, ssize_t start,
-	ssize_t end)
-{
-	ssize_t len, blen;
-	const char *buffer;
-
-	if (start + 1 == end) {
-		/* trivial case, output a decoded list */
-		PyObject *tmp = PyList_GetItem(bins, start);
-		if (!tmp)
-			return NULL;
-		if (PyObject_AsCharBuffer(tmp, &buffer, &blen))
-			return NULL;
-		return mpatch_decode(buffer, blen);
-	}
-
-	/* divide and conquer, memory management is elsewhere */
-	len = (end - start) / 2;
-	return combine(mpatch_fold(bins, start, start + len),
-		       mpatch_fold(bins, start + len, end));
-}
-
 static PyObject *
 patches(PyObject *self, PyObject *args)
 {
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -561,7 +561,8 @@ extmodules = [
               depends=common_depends + ['mercurial/bdiff.h']),
     Extension('mercurial.diffhelpers', ['mercurial/diffhelpers.c'],
               depends=common_depends),
-    Extension('mercurial.mpatch', ['mercurial/mpatch.c'],
+    Extension('mercurial.mpatch', ['mercurial/mpatch.c',
+                                   'mercurial/mpatch_module.c'],
               depends=common_depends),
     Extension('mercurial.parsers', ['mercurial/dirs.c',
                                     'mercurial/manifest.c',