diff --git a/src/collective/dms/mailcontent/indexers.py b/src/collective/dms/mailcontent/indexers.py
new file mode 100644
index 0000000..e02c4f9
--- /dev/null
+++ b/src/collective/dms/mailcontent/indexers.py
@@ -0,0 +1,13 @@
+from five import grok
+
+from plone.indexer import indexer
+
+from collective.dms.mailcontent.dmsmail import IDmsIncomingMail
+
+
+@indexer(IDmsIncomingMail)
+def in_reply_to(obj):
+    """Avoid conflict with plone.app.discussion in_reply_to indexer"""
+    return None
+
+grok.global_adapter(in_reply_to, name='in_reply_to')