diff --git a/python/paddle/trainer/config_parser.py b/python/paddle/trainer/config_parser.py
index 098a51ab8791290d3e0ffa2c3703c724dd2387b9..09c92d3513e86a7657880c01736f5f41f53cfcf6 100644
--- a/python/paddle/trainer/config_parser.py
+++ b/python/paddle/trainer/config_parser.py
@@ -559,6 +559,9 @@ class IdentityOffsetProjection(Projection):
                                                        **xargs)
         self.proj_conf.offset = offset
 
+    def calc_output_size(self, input_layer_config):
+        return 0  # depends on the outside MixedLayer
+
     def calc_parameter_size(self, input_size, output_size):
         return 0