diff -r 20f0c5398e97 Lib/StringIO.py
--- a/Lib/StringIO.py	Mon Feb 04 10:29:38 2013 -0500
+++ b/Lib/StringIO.py	Wed Feb 06 15:36:23 2013 +0200
@@ -158,7 +158,7 @@
             newpos = self.len
         else:
             newpos = i+1
-        if length is not None and length > 0:
+        if length is not None and length >= 0:
             if self.pos + length < newpos:
                 newpos = self.pos + length
         r = self.buf[self.pos:newpos]
diff -r 20f0c5398e97 Lib/test/test_StringIO.py
--- a/Lib/test/test_StringIO.py	Mon Feb 04 10:29:38 2013 -0500
+++ b/Lib/test/test_StringIO.py	Wed Feb 06 15:36:23 2013 +0200
@@ -27,6 +27,8 @@
         eq = self.assertEqual
         self.assertRaises(TypeError, self._fp.seek)
         eq(self._fp.read(10), self._line[:10])
+        eq(self._fp.read(0), '')
+        eq(self._fp.readline(0), '')
         eq(self._fp.readline(), self._line[10:] + '\n')
         eq(len(self._fp.readlines(60)), 2)
         self._fp.seek(0)