diff -r 01676a4c16ff Modules/zipimport.c
--- a/Modules/zipimport.c	Sun Dec 08 10:06:04 2013 +0100
+++ b/Modules/zipimport.c	Sun Dec 08 12:07:33 2013 +0100
@@ -818,16 +818,12 @@ static PyTypeObject ZipImporter_Type = {
    4 bytes, encoded as little endian. This partially reimplements
    marshal.c:r_long() */
 static long
-get_long(unsigned char *buf) {
-    long x;
+get_ulong(unsigned char *buf) {
+    unsigned long x;
     x =  buf[0];
-    x |= (long)buf[1] <<  8;
-    x |= (long)buf[2] << 16;
-    x |= (long)buf[3] << 24;
-#if SIZEOF_LONG > 4
-    /* Sign extension for 64-bit machines */
-    x |= -(x & 0x80000000L);
-#endif
+    x |= (unsigned long)buf[1] <<  8;
+    x |= (unsigned long)buf[2] << 16;
+    x |= (unsigned long)buf[3] << 24;
     return x;
 }
 
@@ -860,10 +856,12 @@ read_directory(PyObject *archive)
     FILE *fp;
     unsigned short flags;
     short compress, time, date, name_size;
-    long crc, data_size, file_size, header_size;
-    Py_ssize_t file_offset, header_position, header_offset;
-    long l, count;
-    Py_ssize_t i;
+    long crc, data_size, file_size;
+    unsigned long header_size, header_offset;
+    Py_ssize_t file_offset, header_position;
+    long l;
+    unsigned long count;
+    size_t i;
     char name[MAXPATHLEN + 5];
     char dummy[8]; /* Buffer to read unused header values into */
     PyObject *nameobj = NULL;
@@ -880,28 +878,25 @@ read_directory(PyObject *archive)
         return NULL;
     }
 
-    if (fseek(fp, -22, SEEK_END) == -1) {
-        fclose(fp);
-        PyErr_Format(ZipImportError, "can't read Zip file: %R", archive);
-        return NULL;
-    }
+    if (fseek(fp, -22, SEEK_END) == -1)
+        goto invalid_header;
     header_position = ftell(fp);
-    if (fread(endof_central_dir, 1, 22, fp) != 22) {
-        fclose(fp);
-        PyErr_Format(ZipImportError, "can't read Zip file: %R", archive);
-        return NULL;
-    }
-    if (get_long((unsigned char *)endof_central_dir) != 0x06054B50) {
+    if (fread(endof_central_dir, 1, 22, fp) != 22)
+        goto invalid_header;
+    if (get_ulong((unsigned char *)endof_central_dir) != 0x06054B50UL)
         /* Bad: End of Central Dir signature */
-        fclose(fp);
-        PyErr_Format(ZipImportError, "not a Zip file: %R", archive);
-        return NULL;
-    }
+        goto invalid_header;
 
-    header_size = get_long((unsigned char *)endof_central_dir + 12);
-    header_offset = get_long((unsigned char *)endof_central_dir + 16);
+    header_size = get_ulong((unsigned char *)endof_central_dir + 12);
+    header_offset = get_ulong((unsigned char *)endof_central_dir + 16);
+    if (header_offset > ULONG_MAX - header_size)
+        goto invalid_header;
+    if (header_position < header_offset + header_size)
+        goto invalid_header;
     arc_offset = header_position - header_offset - header_size;
-    header_offset += arc_offset;
+    if (header_position < header_size)
+        goto invalid_header;
+    header_offset = header_position - header_size;
 
     files = PyDict_New();
     if (files == NULL)
@@ -949,7 +944,7 @@ read_directory(PyObject *archive)
             name_size = MAXPATHLEN;
 
         p = name;
-        for (i = 0; i < (Py_ssize_t)name_size; i++) {
+        for (i = 0; i < (size_t)name_size; i++) {
             *p = (char)getc(fp);
             if (*p == '/')
                 *p = SEP;
@@ -1002,7 +997,7 @@ read_directory(PyObject *archive)
     }
     fclose(fp);
     if (Py_VerboseFlag)
-        PySys_FormatStderr("# zipimport: found %ld names in %R\n",
+        PySys_FormatStderr("# zipimport: found %lu names in %R\n",
                            count, archive);
     return files;
 file_error:
@@ -1011,6 +1006,8 @@ file_error:
     Py_XDECREF(nameobj);
     PyErr_Format(ZipImportError, "can't read Zip file: %R", archive);
     return NULL;
+invalid_header:
+    PyErr_Format(ZipImportError, "not a Zip file: %R", archive);
 error:
     fclose(fp);
     Py_XDECREF(files);
@@ -1196,7 +1193,7 @@ unmarshal_code(PyObject *pathname, PyObj
         return NULL;
     }
 
-    if (get_long((unsigned char *)buf) != PyImport_GetMagicNumber()) {
+    if (get_ulong((unsigned char *)buf) != PyImport_GetMagicNumber()) {
         if (Py_VerboseFlag)
             PySys_FormatStderr("# %R has bad magic\n",
                                pathname);
@@ -1204,7 +1201,7 @@ unmarshal_code(PyObject *pathname, PyObj
         return Py_None;  /* signal caller to try alternative */
     }
 
-    if (mtime != 0 && !eq_mtime(get_long((unsigned char *)buf + 4),
+    if (mtime != 0 && !eq_mtime(get_ulong((unsigned char *)buf + 4),
                                 mtime)) {
         if (Py_VerboseFlag)
             PySys_FormatStderr("# %R has bad mtime\n",