diff -r 84148898a606 Lib/plistlib.py
--- a/Lib/plistlib.py	Sun Dec 01 14:30:47 2013 +0100
+++ b/Lib/plistlib.py	Mon Dec 02 17:34:58 2013 +0200
@@ -665,7 +665,8 @@
             return b''
 
         elif tokenH == 0x10:  # int
-            return int.from_bytes(self._fp.read(1 << tokenL), 'big')
+            return int.from_bytes(self._fp.read(1 << tokenL),
+                                  'big', signed=tokenL >= 3)
 
         elif token == 0x22: # real
             return struct.unpack('>f', self._fp.read(4))[0]
@@ -871,14 +872,20 @@
             self._fp.write(b'\x09')
 
         elif isinstance(value, int):
-            if value < 1 << 8:
-                self._fp.write(struct.pack('>BB', 0x10, value))
-            elif value < 1 << 16:
-                self._fp.write(struct.pack('>BH', 0x11, value))
-            elif value < 1 << 32:
-                self._fp.write(struct.pack('>BL', 0x12, value))
+            if value >= 0:
+                if value < 1 << 8:
+                    self._fp.write(struct.pack('>BB', 0x10, value))
+                    return
+                if value < 1 << 16:
+                    self._fp.write(struct.pack('>BH', 0x11, value))
+                    return
+                if value < 1 << 32:
+                    self._fp.write(struct.pack('>BL', 0x12, value))
+                    return
+            if -1 << 63 <= value < 1 << 63:
+                self._fp.write(struct.pack('>Bq', 0x13, value))
             else:
-                self._fp.write(struct.pack('>BQ', 0x13, value))
+                self._fp.write(b'\x14' + value.to_bytes(16, 'big', signed=True))
 
         elif isinstance(value, float):
             self._fp.write(struct.pack('>Bd', 0x23, value))
diff -r 84148898a606 Lib/test/test_plistlib.py
--- a/Lib/test/test_plistlib.py	Sun Dec 01 14:30:47 2013 +0100
+++ b/Lib/test/test_plistlib.py	Mon Dec 02 17:34:58 2013 +0200
@@ -133,6 +133,16 @@
         self.assertRaises(AttributeError, plistlib.dump, pl, 'filename')
         self.assertRaises(AttributeError, plistlib.load, 'filename')
 
+    def test_int(self):
+        for pl in [0, 2**8-1, 2**8, 2**16-1, 2**16, 2**32-1, 2**32,
+                   2**63-1, 2**63, 2**127-1, -1, -2**63, -2**127]:
+            with self.subTest(pl=pl):
+                data = plistlib.dumps(pl)
+                pl2 = plistlib.loads(data)
+                self.assertIsInstance(pl2, int)
+                self.assertEqual(pl, pl2)
+                data2 = plistlib.dumps(pl2)
+                self.assertEqual(data, data2)
 
     def test_bytes(self):
         pl = self._create()