diff --git a/tools/post_process_props.py b/tools/post_process_props.py
index 78a23fb72d..d8c9cb157f 100755
--- a/tools/post_process_props.py
+++ b/tools/post_process_props.py
@@ -88,6 +88,8 @@ def override_optional_props(prop_list, allow_dup=False):
     if len(overriding_props) > 1:
       # duplicated props are allowed when the all have the same value
       if all(overriding_props[0].value == p.value for p in overriding_props):
+        for p in optional_props:
+          p.delete("overridden by %s" % str(overriding_props[0]))
         continue
       # or if dup is explicitly allowed for compat reason
       if allow_dup:
diff --git a/tools/test_post_process_props.py b/tools/test_post_process_props.py
index 44fe957d74..12d52e566d 100644
--- a/tools/test_post_process_props.py
+++ b/tools/test_post_process_props.py
@@ -221,11 +221,17 @@ class PropListTestcase(unittest.TestCase):
       stderr_redirect = io.StringIO()
       with contextlib.redirect_stderr(stderr_redirect):
         props = PropList("hello")
+        optional_prop = props.get_props("foo")[2] # the last foo?=false one
 
         # we have duplicated foo=true and foo=true, but that's allowed
         # since they have the same value
         self.assertTrue(override_optional_props(props))
 
+        # foo?=false should be commented out
+        self.assertEqual("# Removed by post_process_props.py because " +
+                         "overridden by foo=true\n#foo?=false",
+                         str(optional_prop))
+
   def test_allowDuplicates(self):
     content = """
     # comment