diff --git a/mitogen/core.py b/mitogen/core.py
index fc578c0b..ed18f6ad 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -596,6 +596,23 @@ def import_module(modname):
     return __import__(modname, None, None, [''])
 
 
+def iter_split(buf, delim, func):
+    """
+    Invoke `func(s)` for each `delim`-delimited chunk in the potentially large
+    `buf`, avoiding intermediate lists and quadratic copies. Return the
+    trailing undelimited portion of `buf`.
+    """
+    start = 0
+    while True:
+        nl = buf.find(delim, start)
+        if nl == -1:
+            break
+        func(buf[start:nl])
+        start = nl + 1
+
+    return buf[start:]
+
+
 class Py24Pickler(py_pickle.Pickler):
     """
     Exceptions were classic classes until Python 2.5. Sadly for 2.4, cPickle
@@ -2427,18 +2444,6 @@ class IoLogger(BasicStream):
     def __repr__(self):
         return '<IoLogger %s>' % (self._name,)
 
-    def _log_lines(self, buf):
-        start = 0
-        while True:
-            nl = min(buf.find('\n', start), start+1024)
-            if nl == -1:
-                break
-            self._log.info('%s', buf[start:nl])
-            start = nl + 1
-
-        if start:
-            self._trailer = buf[start:]
-
     def on_shutdown(self, broker):
         """Shut down the write end of the logging socket."""
         _v and LOG.debug('%r.on_shutdown()', self)
@@ -2454,7 +2459,11 @@ class IoLogger(BasicStream):
         if not buf:
             return self.on_disconnect(broker)
 
-        self._log_lines(self._trailer + buf.decode('latin1'))
+        self._trailer = iter_split(
+            buf=self._trailer + buf.decode('latin1'),
+            delim='\n',
+            func=lambda s: self._log.info('%s', s)
+        )
 
 
 class Router(object):
diff --git a/tests/iter_split_test.py b/tests/iter_split_test.py
new file mode 100644
index 00000000..a385b2f1
--- /dev/null
+++ b/tests/iter_split_test.py
@@ -0,0 +1,41 @@
+
+import mock
+import unittest2
+
+import mitogen.core
+
+import testlib
+
+
+class IterSplitTest(unittest2.TestCase):
+    func = staticmethod(mitogen.core.iter_split)
+
+    def test_empty_buffer(self):
+        lst = []
+        trailer = self.func(buf='', delim='\n', func=lst.append)
+        self.assertEquals('', trailer)
+        self.assertEquals([], lst)
+
+    def test_empty_line(self):
+        lst = []
+        trailer = self.func(buf='\n', delim='\n', func=lst.append)
+        self.assertEquals('', trailer)
+        self.assertEquals([''], lst)
+
+    def test_one_line(self):
+        buf = 'xxxx\n'
+        lst = []
+        trailer = self.func(buf=buf, delim='\n', func=lst.append)
+        self.assertEquals('', trailer)
+        self.assertEquals(lst, ['xxxx'])
+
+    def test_one_incomplete(self):
+        buf = 'xxxx\nyy'
+        lst = []
+        trailer = self.func(buf=buf, delim='\n', func=lst.append)
+        self.assertEquals('yy', trailer)
+        self.assertEquals(lst, ['xxxx'])
+
+
+if __name__ == '__main__':
+    unittest2.main()