diff --git a/tools/patman/commit.py b/tools/patman/commit.py
index 48d0529..8d583c4 100644
--- a/tools/patman/commit.py
+++ b/tools/patman/commit.py
@@ -2,6 +2,7 @@
 # Copyright (c) 2011 The Chromium OS Authors.
 #
 
+import collections
 import re
 
 # Separates a tag: at the beginning of the subject from the rest of it
@@ -23,6 +24,9 @@
         notes: List of lines in the commit (not series) notes
         change_id: the Change-Id: tag that was stripped from this commit
             and can be used to generate the Message-Id.
+        rtags: Response tags (e.g. Reviewed-by) collected by the commit, dict:
+            key: rtag type (e.g. 'Reviewed-by')
+            value: Set of people who gave that rtag, each a name/email string
     """
     def __init__(self, hash):
         self.hash = hash
@@ -33,6 +37,7 @@
         self.signoff_set = set()
         self.notes = []
         self.change_id = None
+        self.rtags = collections.defaultdict(set)
 
     def AddChange(self, version, info):
         """Add a new change line to the change list for a version.
@@ -88,3 +93,12 @@
           return False
         self.signoff_set.add(signoff)
         return True
+
+    def AddRtag(self, rtag_type, who):
+        """Add a response tag to a commit
+
+        Args:
+            key: rtag type (e.g. 'Reviewed-by')
+            who: Person who gave that rtag, e.g. 'Fred Bloggs <fred@bloggs.org>'
+        """
+        self.rtags[rtag_type].add(who)