diff --git a/synapse/state.py b/synapse/state.py
index 38adde4dc9..99f873b6e5 100644
--- a/synapse/state.py
+++ b/synapse/state.py
@@ -263,9 +263,10 @@ class StateHandler(object):
         }
 
         if event_type:
-            prev_states = conflicted_state.get(
-                (event_type, state_key), {}
-            ).keys()
+            prev_states_events = conflicted_state.get(
+                (event_type, state_key), []
+            )
+            prev_states = [s.event_id for s in prev_states_events]
         else:
             prev_states = []