diff --git a/IPython/core/inputsplitter.py b/IPython/core/inputsplitter.py
index c54f922..670f468 100644
--- a/IPython/core/inputsplitter.py
+++ b/IPython/core/inputsplitter.py
@@ -603,7 +603,9 @@ class InputSplitter(object):
 
         If input lines are not newline-terminated, a newline is automatically
         appended."""
-
+        if not isinstance(lines, unicode):
+            lines = lines.decode(self.encoding)
+        
         if buffer is None:
             buffer = self._buffer