diff --git a/mitogen/core.py b/mitogen/core.py
index 974b5209..0f0b5992 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -455,20 +455,20 @@ def io_op(func, *args):
       signalled by :data:`errno.EPIPE`.
 
     :returns:
-        Tuple of `(return_value, disconnected)`, where `return_value` is the
-        return value of `func(*args)`, and `disconnected` is :data:`True` if
-        disconnection was detected, otherwise :data:`False`.
+        Tuple of `(return_value, disconnect_reason)`, where `return_value` is
+        the return value of `func(*args)`, and `disconnected` is an exception
+        instance when disconnection was detected, otherwise :data:`None`.
     """
     while True:
         try:
-            return func(*args), False
+            return func(*args), None
         except (select.error, OSError, IOError):
             e = sys.exc_info()[1]
             _vv and IOLOG.debug('io_op(%r) -> OSError: %s', func, e)
             if e.args[0] == errno.EINTR:
                 continue
             if e.args[0] in (errno.EIO, errno.ECONNRESET, errno.EPIPE):
-                return None, True
+                return None, e
             raise
 
 
diff --git a/mitogen/parent.py b/mitogen/parent.py
index 2a864fa1..e4b1f66a 100644
--- a/mitogen/parent.py
+++ b/mitogen/parent.py
@@ -544,7 +544,8 @@ class IteratingRead(object):
             for fd in self.poller.poll(self.timeout):
                 s, disconnected = mitogen.core.io_op(os.read, fd, 4096)
                 if disconnected or not s:
-                    IOLOG.debug('iter_read(%r) -> disconnected', fd)
+                    LOG.debug('iter_read(%r) -> disconnected: %s',
+                              fd, disconnected)
                     self.poller.stop_receive(fd)
                 else:
                     IOLOG.debug('iter_read(%r) -> %r', fd, s)