diff --git a/im2txt/im2txt/inference_utils/caption_generator.py b/im2txt/im2txt/inference_utils/caption_generator.py
index a6ceecc73ab..4488e6f00d0 100644
--- a/im2txt/im2txt/inference_utils/caption_generator.py
+++ b/im2txt/im2txt/inference_utils/caption_generator.py
@@ -54,6 +54,16 @@ def __cmp__(self, other):
       return -1
     else:
       return 1
+  
+  # for version 3 compatibility (__cmp__ is deprecated)
+  def __lt__(self, other):
+    assert isinstance(other, Caption)
+    return self.score < other.score
+  
+  # also for version 3 compatibility
+  def __eq__(self, other):
+    assert isinstance(other, Caption)
+    return self.score == other.score
 
 
 class TopN(object):