diff --git a/Lib/StringIO.py b/Lib/StringIO.py
index 232009f..300dd5a 100644
--- a/Lib/StringIO.py
+++ b/Lib/StringIO.py
@@ -158,7 +158,7 @@
             newpos = self.len
         else:
             newpos = i+1
-        if length is not None:
+        if length is not None and length > 0:
             if self.pos + length < newpos:
                 newpos = self.pos + length
         r = self.buf[self.pos:newpos]