diff --git a/changelog.d/5203.feature b/changelog.d/5203.feature
new file mode 100644
index 0000000000..747098c166
--- /dev/null
+++ b/changelog.d/5203.feature
@@ -0,0 +1 @@
+Add experimental support for relations (aka reactions and edits).
diff --git a/synapse/storage/relations.py b/synapse/storage/relations.py
index 7d51b38d77..4c83800cca 100644
--- a/synapse/storage/relations.py
+++ b/synapse/storage/relations.py
@@ -280,7 +280,7 @@ class RelationsWorkerStore(SQLBaseStore):
             having_clause = ""
 
         sql = """
-            SELECT type, aggregation_key, COUNT(*), MAX(stream_ordering)
+            SELECT type, aggregation_key, COUNT(DISTINCT sender), MAX(stream_ordering)
             FROM event_relations
             INNER JOIN events USING (event_id)
             WHERE {where_clause}