diff --git a/benches/state_res_bench.rs b/benches/state_res_bench.rs
index ff5c37cc..86d55ff1 100644
--- a/benches/state_res_bench.rs
+++ b/benches/state_res_bench.rs
@@ -48,11 +48,12 @@ fn resolution_shallow_auth_chain(c: &mut Criterion) {
         let (state_at_bob, state_at_charlie, _) = store.set_up();
 
         b.iter(|| {
+            let mut ev_map = state_res::EventMap::default();
             let _resolved = match StateResolution::resolve(
                 &room_id(),
                 &RoomVersionId::Version6,
                 &[state_at_bob.clone(), state_at_charlie.clone()],
-                None,
+                &mut ev_map,
                 &store,
             ) {
                 Ok(state) => state,
@@ -102,7 +103,7 @@ fn resolve_deeper_event_set(c: &mut Criterion) {
                 &room_id(),
                 &RoomVersionId::Version6,
                 &[state_set_a.clone(), state_set_b.clone()],
-                Some(inner.clone()),
+                &mut inner,
                 &store,
             ) {
                 Ok(state) => state,
diff --git a/src/event_auth.rs b/src/event_auth.rs
index 74b363ce..eaf6ef57 100644
--- a/src/event_auth.rs
+++ b/src/event_auth.rs
@@ -193,7 +193,9 @@ pub fn auth_check<E: Event>(
         }
 
         if !valid_membership_change(
-            incoming_event,
+            incoming_event.state_key().as_deref(),
+            incoming_event.sender(),
+            incoming_event.content(),
             prev_event,
             current_third_party_invite,
             &auth_events,
@@ -271,25 +273,27 @@ pub fn auth_check<E: Event>(
 /// this is generated by calling `auth_types_for_event` with the membership event and
 /// the current State.
 pub fn valid_membership_change<E: Event>(
-    user: &Arc<E>,
+    user_state_key: Option<&str>,
+    user_sender: &UserId,
+    content: serde_json::Value,
     prev_event: Option<Arc<E>>,
     current_third_party_invite: Option<Arc<E>>,
     auth_events: &StateMap<Arc<E>>,
 ) -> Result<bool> {
-    let state_key = if let Some(s) = user.state_key() {
+    let state_key = if let Some(s) = user_state_key {
         s
     } else {
         return Err(Error::InvalidPdu("State event requires state_key".into()));
     };
 
-    let content = serde_json::from_value::<room::member::MemberEventContent>(user.content())?;
+    let content = serde_json::from_value::<room::member::MemberEventContent>(content)?;
 
     let target_membership = content.membership;
 
-    let target_user_id = UserId::try_from(state_key.as_str())
-        .map_err(|e| Error::ConversionError(format!("{}", e)))?;
+    let target_user_id =
+        UserId::try_from(state_key).map_err(|e| Error::ConversionError(format!("{}", e)))?;
 
-    let key = (EventType::RoomMember, Some(user.sender().to_string()));
+    let key = (EventType::RoomMember, Some(user_sender.to_string()));
     let sender = auth_events.get(&key);
     let sender_membership =
         sender.map_or(Ok::<_, Error>(member::MembershipState::Leave), |pdu| {
@@ -333,7 +337,7 @@ pub fn valid_membership_change<E: Event>(
         },
     )?;
 
-    let sender_power = power_levels.users.get(&user.sender()).map_or_else(
+    let sender_power = power_levels.users.get(user_sender).map_or_else(
         || {
             if sender_membership != member::MembershipState::Join {
                 None
@@ -372,7 +376,7 @@ pub fn valid_membership_change<E: Event>(
     }
 
     Ok(if target_membership == MembershipState::Join {
-        if user.sender() != &target_user_id {
+        if user_sender != &target_user_id {
             false
         } else if let MembershipState::Ban = current_membership {
             false
@@ -388,7 +392,12 @@ pub fn valid_membership_change<E: Event>(
             if current_membership == MembershipState::Ban {
                 false
             } else {
-                verify_third_party_invite(user, &tp_id, current_third_party_invite)
+                verify_third_party_invite(
+                    Some(state_key),
+                    user_sender,
+                    &tp_id,
+                    current_third_party_invite,
+                )
             }
         } else if sender_membership != MembershipState::Join
             || current_membership == MembershipState::Join
@@ -401,7 +410,7 @@ pub fn valid_membership_change<E: Event>(
                 .is_some()
         }
     } else if target_membership == MembershipState::Leave {
-        if user.sender() == &target_user_id {
+        if user_sender == &target_user_id {
             current_membership == MembershipState::Join
                 || current_membership == MembershipState::Invite
         } else if sender_membership != MembershipState::Join
@@ -791,14 +800,15 @@ pub fn can_send_invite<E: Event>(event: &Arc<E>, auth_events: &StateMap<Arc<E>>)
 }
 
 pub fn verify_third_party_invite<E: Event>(
-    event: &Arc<E>,
+    user_state_key: Option<&str>,
+    sender: &UserId,
     tp_id: &member::ThirdPartyInvite,
     current_third_party_invite: Option<Arc<E>>,
 ) -> bool {
     // 1. check for user being banned happens before this is called
     // checking for mxid and token keys is done by ruma when deserializing
 
-    if event.state_key() != Some(tp_id.signed.mxid.to_string()) {
+    if user_state_key != Some(tp_id.signed.mxid.as_str()) {
         return false;
     }
 
@@ -809,7 +819,7 @@ pub fn verify_third_party_invite<E: Event>(
             return false;
         }
 
-        if event.sender() != current_tpid.sender() {
+        if sender != current_tpid.sender() {
             return false;
         }
 
diff --git a/src/lib.rs b/src/lib.rs
index f2c92753..de68bac3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -46,17 +46,12 @@ impl StateResolution {
         room_version: &RoomVersionId,
         incoming_event: Arc<E>,
         current_state: &StateMap<EventId>,
-        event_map: Option<EventMap<Arc<E>>>,
+        event_map: &mut EventMap<Arc<E>>,
         store: &dyn StateStore<E>,
     ) -> Result<bool> {
         tracing::info!("Applying a single event, state resolution starting");
         let ev = incoming_event;
 
-        let mut event_map = if let Some(ev_map) = event_map {
-            ev_map
-        } else {
-            EventMap::new()
-        };
         let prev_event = if let Some(id) = ev.prev_events().first() {
             store.get_event(room_id, id).ok()
         } else {
@@ -69,7 +64,7 @@ impl StateResolution {
         {
             if let Some(ev_id) = current_state.get(&key) {
                 if let Some(event) =
-                    StateResolution::get_or_load_event(room_id, ev_id, &mut event_map, store)
+                    StateResolution::get_or_load_event(room_id, ev_id, event_map, store)
                 {
                     // TODO synapse checks `rejected_reason` is None here
                     auth_events.insert(key.clone(), event);
@@ -102,17 +97,11 @@ impl StateResolution {
         room_id: &RoomId,
         room_version: &RoomVersionId,
         state_sets: &[StateMap<EventId>],
-        // TODO: make the `Option<&mut EventMap<Arc<ServerPdu>>>`
-        event_map: Option<EventMap<Arc<E>>>,
+        event_map: &mut EventMap<Arc<E>>,
         store: &dyn StateStore<E>,
     ) -> Result<StateMap<EventId>> {
         tracing::info!("State resolution starting");
 
-        let mut event_map = if let Some(ev_map) = event_map {
-            ev_map
-        } else {
-            EventMap::new()
-        };
         // split non-conflicting and conflicting state
         let (clean, conflicting) = StateResolution::separate(&state_sets);
 
@@ -178,7 +167,7 @@ impl StateResolution {
         let mut sorted_control_levels = StateResolution::reverse_topological_power_sort(
             room_id,
             &control_events,
-            &mut event_map,
+            event_map,
             store,
             &all_conflicted,
         );
@@ -197,7 +186,7 @@ impl StateResolution {
             room_version,
             &sorted_control_levels,
             &clean,
-            &mut event_map,
+            event_map,
             store,
         )?;
 
@@ -238,7 +227,7 @@ impl StateResolution {
             room_id,
             &events_to_resolve,
             power_event,
-            &mut event_map,
+            event_map,
             store,
         );
 
@@ -255,7 +244,7 @@ impl StateResolution {
             room_version,
             &sorted_left_events,
             &resolved_control, // The control events are added to the final resolved state
-            &mut event_map,
+            event_map,
             store,
         )?;
 
diff --git a/tests/event_auth.rs b/tests/event_auth.rs
index fb6989b7..46270ca7 100644
--- a/tests/event_auth.rs
+++ b/tests/event_auth.rs
@@ -36,7 +36,15 @@ fn test_ban_pass() {
         &vec![event_id("IMC")],
     );
 
-    assert!(valid_membership_change(&requester, prev, None, &auth_events).unwrap())
+    assert!(valid_membership_change(
+        requester.state_key().as_deref(),
+        requester.sender(),
+        requester.content(),
+        prev,
+        None,
+        &auth_events
+    )
+    .unwrap())
 }
 
 #[test]
@@ -63,5 +71,13 @@ fn test_ban_fail() {
         &vec![event_id("IMC")],
     );
 
-    assert!(!valid_membership_change(&requester, prev, None, &auth_events).unwrap())
+    assert!(!valid_membership_change(
+        requester.state_key().as_deref(),
+        requester.sender(),
+        requester.content(),
+        prev,
+        None,
+        &auth_events
+    )
+    .unwrap())
 }
diff --git a/tests/res_with_auth_ids.rs b/tests/res_with_auth_ids.rs
index cc123208..627750e2 100644
--- a/tests/res_with_auth_ids.rs
+++ b/tests/res_with_auth_ids.rs
@@ -41,11 +41,17 @@ fn ban_with_auth_chains() {
 fn base_with_auth_chains() {
     let store = TestStore(INITIAL_EVENTS());
 
-    let resolved: BTreeMap<_, EventId> =
-        match StateResolution::resolve(&room_id(), &RoomVersionId::Version6, &[], None, &store) {
-            Ok(state) => state,
-            Err(e) => panic!("{}", e),
-        };
+    let mut ev_map = state_res::EventMap::default();
+    let resolved: BTreeMap<_, EventId> = match StateResolution::resolve(
+        &room_id(),
+        &RoomVersionId::Version6,
+        &[],
+        &mut ev_map,
+        &store,
+    ) {
+        Ok(state) => state,
+        Err(e) => panic!("{}", e),
+    };
 
     let resolved = resolved
         .values()
@@ -105,11 +111,12 @@ fn ban_with_auth_chains2() {
     .map(|ev| ((ev.kind(), ev.state_key()), ev.event_id().clone()))
     .collect::<StateMap<_>>();
 
+    let mut ev_map = state_res::EventMap::default();
     let resolved: StateMap<EventId> = match StateResolution::resolve(
         &room_id(),
         &RoomVersionId::Version6,
         &[state_set_a, state_set_b],
-        None,
+        &mut ev_map,
         &store,
     ) {
         Ok(state) => state,
diff --git a/tests/state_res.rs b/tests/state_res.rs
index 044d0811..f85f7eec 100644
--- a/tests/state_res.rs
+++ b/tests/state_res.rs
@@ -265,11 +265,12 @@ fn test_event_map_none() {
     // build up the DAG
     let (state_at_bob, state_at_charlie, expected) = store.set_up();
 
+    let mut ev_map = state_res::EventMap::default();
     let resolved = match StateResolution::resolve(
         &room_id(),
         &RoomVersionId::Version2,
         &[state_at_bob, state_at_charlie],
-        None,
+        &mut ev_map,
         &store,
     ) {
         Ok(state) => state,
diff --git a/tests/utils.rs b/tests/utils.rs
index bed80160..bec72356 100644
--- a/tests/utils.rs
+++ b/tests/utils.rs
@@ -114,7 +114,7 @@ pub fn do_check(
                 &room_id(),
                 &RoomVersionId::Version6,
                 &state_sets,
-                Some(event_map.clone()),
+                &mut event_map,
                 &store,
             );
             match resolved {