diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index 1ebccdf..297bb07 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -91,8 +91,8 @@
 typedef struct {
     PyObject_HEAD
     char *      data;
-    size_t      size;
-    size_t      pos;    /* relative to offset */
+    Py_ssize_t  size;
+    Py_ssize_t  pos;    /* relative to offset */
 #ifdef MS_WINDOWS
     PY_LONG_LONG offset;
 #else
@@ -204,33 +204,32 @@
                       PyObject *unused)
 {
     CHECK_VALID(NULL);
-    if (self->pos < self->size) {
-        char value = self->data[self->pos];
-        self->pos += 1;
-        return Py_BuildValue("c", value);
-    } else {
+    if (self->pos >= self->size) {
         PyErr_SetString(PyExc_ValueError, "read byte out of range");
         return NULL;
     }
+    return PyString_FromStringAndSize(&self->data[self->pos++], 1);
 }
 
 static PyObject *
 mmap_read_line_method(mmap_object *self,
                       PyObject *unused)
 {
-    char *start = self->data+self->pos;
-    char *eof = self->data+self->size;
-    char *eol;
+    Py_ssize_t remaining;
+    char *start, *eol;
     PyObject *result;
 
     CHECK_VALID(NULL);
 
-    eol = memchr(start, '\n', self->size - self->pos);
+    remaining = (self->pos < self->size) ? self->size - self->pos : 0;
+    if (!remaining)
+        return PyString_FromString("");
+    start = self->data + self->pos;
+    eol = memchr(start, '\n', remaining);
     if (!eol)
-        eol = eof;
+        eol = self->data + self->size;
     else
-        ++eol;                  /* we're interested in the position after the
-                           newline. */
+        ++eol; /* advance past newline */
     result = PyString_FromStringAndSize(start, (eol - start));
     self->pos += (eol - start);
     return result;
@@ -240,28 +239,18 @@
 mmap_read_method(mmap_object *self,
                  PyObject *args)
 {
-    Py_ssize_t num_bytes, n;
+    Py_ssize_t num_bytes, remaining;
     PyObject *result;
 
     CHECK_VALID(NULL);
     if (!PyArg_ParseTuple(args, "n:read", &num_bytes))
-        return(NULL);
+        return NULL;
 
     /* silently 'adjust' out-of-range requests */
-    assert(self->size >= self->pos);
-    n = self->size - self->pos;
-    /* The difference can overflow, only if self->size is greater than
-     * PY_SSIZE_T_MAX.  But then the operation cannot possibly succeed,
-     * because the mapped area and the returned string each need more
-     * than half of the addressable memory.  So we clip the size, and let
-     * the code below raise MemoryError.
-     */
-    if (n < 0)
-        n = PY_SSIZE_T_MAX;
-    if (num_bytes < 0 || num_bytes > n) {
-        num_bytes = n;
-    }
-    result = Py_BuildValue("s#", self->data+self->pos, num_bytes);
+    remaining = (self->pos < self->size) ? self->size - self->pos : 0;
+    if (num_bytes < 0 || num_bytes > remaining)
+        num_bytes = remaining;
+    result = PyString_FromStringAndSize(&self->data[self->pos], num_bytes);
     self->pos += num_bytes;
     return result;
 }
@@ -288,14 +277,14 @@
             start += self->size;
         if (start < 0)
             start = 0;
-        else if ((size_t)start > self->size)
+        else if (start > self->size)
             start = self->size;
 
         if (end < 0)
             end += self->size;
         if (end < 0)
             end = 0;
-        else if ((size_t)end > self->size)
+        else if (end > self->size)
             end = self->size;
 
         start_p = self->data + start;
@@ -362,12 +351,12 @@
     if (!is_writeable(self))
         return NULL;
 
-    if ((self->pos + length) > self->size) {
+    if (self->pos > self->size || self->size - self->pos < length) {
         PyErr_SetString(PyExc_ValueError, "data out of range");
         return NULL;
     }
-    memcpy(self->data+self->pos, data, length);
-    self->pos = self->pos+length;
+    memcpy(&self->data[self->pos], data, length);
+    self->pos += length;
     Py_INCREF(Py_None);
     return Py_None;
 }
@@ -386,8 +375,7 @@
         return NULL;
 
     if (self->pos < self->size) {
-        *(self->data+self->pos) = value;
-        self->pos += 1;
+        self->data[self->pos++] = value;
         Py_INCREF(Py_None);
         return Py_None;
     }
@@ -458,8 +446,14 @@
     if (!PyArg_ParseTuple(args, "n:resize", &new_size) ||
         !is_resizeable(self)) {
         return NULL;
+    }
+    if (new_size < 0 || PY_SSIZE_T_MAX - new_size < self->offset) {
+        PyErr_SetString(PyExc_ValueError, "new size out of range");
+        return NULL;
+    }
+
+    {
 #ifdef MS_WINDOWS
-    } else {
         DWORD dwErrCode = 0;
         DWORD off_hi, off_lo, newSizeLow, newSizeHigh;
         /* First, unmap the file view */
@@ -509,15 +503,13 @@
 
 #ifdef UNIX
 #ifndef HAVE_MREMAP
-    } else {
         PyErr_SetString(PyExc_SystemError,
                         "mmap: resizing not available--no mremap()");
         return NULL;
 #else
-    } else {
         void *newmap;
 
-        if (ftruncate(self->fd, self->offset + new_size) == -1) {
+        if (self->fd != -1 && ftruncate(self->fd, self->offset + new_size) == -1) {
             PyErr_SetFromErrno(mmap_module_error);
             return NULL;
         }
@@ -525,11 +517,11 @@
 #ifdef MREMAP_MAYMOVE
         newmap = mremap(self->data, self->size, new_size, MREMAP_MAYMOVE);
 #else
-        #if defined(__NetBSD__)
-            newmap = mremap(self->data, self->size, self->data, new_size, 0);
-        #else
-            newmap = mremap(self->data, self->size, new_size, 0);
-        #endif /* __NetBSD__ */
+#if defined(__NetBSD__)
+        newmap = mremap(self->data, self->size, self->data, new_size, 0);
+#else
+        newmap = mremap(self->data, self->size, new_size, 0);
+#endif /* __NetBSD__ */
 #endif
         if (newmap == (void *)-1)
         {
@@ -560,7 +552,7 @@
     CHECK_VALID(NULL);
     if (!PyArg_ParseTuple(args, "|nn:flush", &offset, &size))
         return NULL;
-    if ((size_t)(offset + size) > self->size) {
+    if (size < 0 || offset < 0 || self->size - offset < size) {
         PyErr_SetString(PyExc_ValueError, "flush values out of range");
         return NULL;
     }
@@ -601,12 +593,12 @@
             where = dist;
             break;
         case 1: /* relative to current position */
-            if ((Py_ssize_t)self->pos + dist < 0)
+            if (PY_SSIZE_T_MAX - self->pos < dist)
                 goto onoutofrange;
             where = self->pos + dist;
             break;
         case 2: /* relative to end */
-            if ((Py_ssize_t)self->size + dist < 0)
+            if (PY_SSIZE_T_MAX - self->size < dist)
                 goto onoutofrange;
             where = self->size + dist;
             break;
@@ -629,23 +621,27 @@
 static PyObject *
 mmap_move_method(mmap_object *self, PyObject *args)
 {
-    unsigned long dest, src, cnt;
+    Py_ssize_t dest, src, cnt;
     CHECK_VALID(NULL);
-    if (!PyArg_ParseTuple(args, "kkk:move", &dest, &src, &cnt) ||
+    if (!PyArg_ParseTuple(args, "nnn:move", &dest, &src, &cnt) ||
         !is_writeable(self)) {
         return NULL;
     } else {
         /* bounds check the values */
-        if (cnt < 0 || (cnt + dest) < cnt || (cnt + src) < cnt ||
-           src < 0 || src > self->size || (src + cnt) > self->size ||
-           dest < 0 || dest > self->size || (dest + cnt) > self->size) {
-            PyErr_SetString(PyExc_ValueError,
-                "source, destination, or count out of range");
-            return NULL;
-        }
-        memmove(self->data+dest, self->data+src, cnt);
+        if (dest < 0 || src < 0 || cnt < 0)
+            goto bounds;
+        if (self->size - dest < cnt || self->size - src < cnt)
+            goto bounds;
+
+        memmove(&self->data[dest], &self->data[src], cnt);
+
         Py_INCREF(Py_None);
         return Py_None;
+
+      bounds:
+        PyErr_SetString(PyExc_ValueError,
+                        "source, destination, or count out of range");
+        return NULL;
     }
 }
 
@@ -745,7 +741,7 @@
 mmap_item(mmap_object *self, Py_ssize_t i)
 {
     CHECK_VALID(NULL);
-    if (i < 0 || (size_t)i >= self->size) {
+    if (i < 0 || i >= self->size) {
         PyErr_SetString(PyExc_IndexError, "mmap index out of range");
         return NULL;
     }
@@ -758,13 +754,13 @@
     CHECK_VALID(NULL);
     if (ilow < 0)
         ilow = 0;
-    else if ((size_t)ilow > self->size)
+    else if (ilow > self->size)
         ilow = self->size;
     if (ihigh < 0)
         ihigh = 0;
     if (ihigh < ilow)
         ihigh = ilow;
-    else if ((size_t)ihigh > self->size)
+    else if (ihigh > self->size)
         ihigh = self->size;
 
     return PyString_FromStringAndSize(self->data + ilow, ihigh-ilow);
@@ -780,7 +776,7 @@
             return NULL;
         if (i < 0)
             i += self->size;
-        if (i < 0 || (size_t)i >= self->size) {
+        if (i < 0 || i >= self->size) {
             PyErr_SetString(PyExc_IndexError,
                 "mmap index out of range");
             return NULL;
@@ -850,13 +846,13 @@
     CHECK_VALID(-1);
     if (ilow < 0)
         ilow = 0;
-    else if ((size_t)ilow > self->size)
+    else if (ilow > self->size)
         ilow = self->size;
     if (ihigh < 0)
         ihigh = 0;
     if (ihigh < ilow)
         ihigh = ilow;
-    else if ((size_t)ihigh > self->size)
+    else if (ihigh > self->size)
         ihigh = self->size;
 
     if (v == NULL) {
@@ -887,7 +883,7 @@
     const char *buf;
 
     CHECK_VALID(-1);
-    if (i < 0 || (size_t)i >= self->size) {
+    if (i < 0 || i >= self->size) {
         PyErr_SetString(PyExc_IndexError, "mmap index out of range");
         return -1;
     }
@@ -921,7 +917,7 @@
             return -1;
         if (i < 0)
             i += self->size;
-        if (i < 0 || (size_t)i >= self->size) {
+        if (i < 0 || i >= self->size) {
             PyErr_SetString(PyExc_IndexError,
                 "mmap index out of range");
             return -1;
@@ -1092,32 +1088,6 @@
 };
 
 
-/* extract the map size from the given PyObject
-
-   Returns -1 on error, with an appropriate Python exception raised. On
-   success, the map size is returned. */
-static Py_ssize_t
-_GetMapSize(PyObject *o, const char* param)
-{
-    if (o == NULL)
-        return 0;
-    if (PyIndex_Check(o)) {
-        Py_ssize_t i = PyNumber_AsSsize_t(o, PyExc_OverflowError);
-        if (i==-1 && PyErr_Occurred())
-            return -1;
-        if (i < 0) {
-            PyErr_Format(PyExc_OverflowError,
-                            "memory mapped %s must be positive",
-                            param);
-            return -1;
-        }
-        return i;
-    }
-
-    PyErr_SetString(PyExc_TypeError, "map size must be an integral value");
-    return -1;
-}
-
 #ifdef UNIX
 #ifdef HAVE_LARGEFILE_SUPPORT
 #define _Py_PARSE_OFF_T "L"
@@ -1132,7 +1102,6 @@
     struct stat st;
 #endif
     mmap_object *m_obj;
-    PyObject *map_size_obj = NULL;
     Py_ssize_t map_size;
     off_t offset = 0;
     int fd, flags = MAP_SHARED, prot = PROT_WRITE | PROT_READ;
@@ -1142,13 +1111,15 @@
                                      "flags", "prot",
                                      "access", "offset", NULL};
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwdict, "iO|iii" _Py_PARSE_OFF_T, keywords,
-                                     &fd, &map_size_obj, &flags, &prot,
+    if (!PyArg_ParseTupleAndKeywords(args, kwdict, "in|iii" _Py_PARSE_OFF_T, keywords,
+                                     &fd, &map_size, &flags, &prot,
                                      &access, &offset))
         return NULL;
-    map_size = _GetMapSize(map_size_obj, "size");
-    if (map_size < 0)
+    if (map_size < 0) {
+        PyErr_SetString(PyExc_OverflowError,
+                        "memory mapped length must be postiive");
         return NULL;
+    }
     if (offset < 0) {
         PyErr_SetString(PyExc_OverflowError,
             "memory mapped offset must be positive");
@@ -1220,7 +1191,7 @@
                 return NULL;
             }
             map_size = (Py_ssize_t) (st.st_size - offset);
-        } else if (offset + (size_t)map_size > st.st_size) {
+        } else if (offset > st.st_size || st.st_size - offset < map_size) {
             PyErr_SetString(PyExc_ValueError,
                             "mmap length is greater than file size");
             return NULL;
@@ -1230,8 +1201,8 @@
     m_obj = (mmap_object *)type->tp_alloc(type, 0);
     if (m_obj == NULL) {return NULL;}
     m_obj->data = NULL;
-    m_obj->size = (size_t) map_size;
-    m_obj->pos = (size_t) 0;
+    m_obj->size = map_size;
+    m_obj->pos = 0;
     m_obj->offset = offset;
     if (fd == -1) {
         m_obj->fd = -1;
@@ -1290,7 +1261,6 @@
 new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
 {
     mmap_object *m_obj;
-    PyObject *map_size_obj = NULL;
     Py_ssize_t map_size;
     PY_LONG_LONG offset = 0, size;
     DWORD off_hi;       /* upper 32 bits of offset */
@@ -1307,8 +1277,8 @@
                                       "tagname",
                                       "access", "offset", NULL };
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwdict, "iO|ziL", keywords,
-                                     &fileno, &map_size_obj,
+    if (!PyArg_ParseTupleAndKeywords(args, kwdict, "in|ziL", keywords,
+                                     &fileno, &map_size,
                                      &tagname, &access, &offset)) {
         return NULL;
     }
@@ -1331,9 +1301,11 @@
                             "mmap invalid access parameter.");
     }
 
-    map_size = _GetMapSize(map_size_obj, "size");
-    if (map_size < 0)
+    if (map_size < 0) {
+        PyErr_SetString(PyExc_OverflowError,
+                        "memory mapped length must be postiive");
         return NULL;
+    }
     if (offset < 0) {
         PyErr_SetString(PyExc_OverflowError,
             "memory mapped offset must be positive");