diff --git a/crates/ruma-state-res/benches/state_res_bench.rs b/crates/ruma-state-res/benches/state_res_bench.rs
index 2673eded..508f8be6 100644
--- a/crates/ruma-state-res/benches/state_res_bench.rs
+++ b/crates/ruma-state-res/benches/state_res_bench.rs
@@ -46,7 +46,7 @@ fn lexico_topo_sort(c: &mut Criterion) {
         };
         b.iter(|| {
             let _ = StateResolution::lexicographical_topological_sort(&graph, |id| {
-                (0, MilliSecondsSinceUnixEpoch(uint!(0)), id.clone())
+                Ok((0, MilliSecondsSinceUnixEpoch(uint!(0)), id.clone()))
             });
         })
     });
diff --git a/crates/ruma-state-res/src/lib.rs b/crates/ruma-state-res/src/lib.rs
index 91c49227..b60e691a 100644
--- a/crates/ruma-state-res/src/lib.rs
+++ b/crates/ruma-state-res/src/lib.rs
@@ -136,7 +136,7 @@ impl StateResolution {
             &control_events,
             &all_conflicted,
             &fetch_event,
-        );
+        )?;
 
         debug!("sorted control events: {}", sorted_control_levels.len());
         trace!("{:?}", sorted_control_levels);
@@ -174,7 +174,7 @@ impl StateResolution {
         debug!("power event: {:?}", power_event);
 
         let sorted_left_events =
-            StateResolution::mainline_sort(&events_to_resolve, power_event, &fetch_event);
+            StateResolution::mainline_sort(&events_to_resolve, power_event, &fetch_event)?;
 
         trace!("events left, sorted: {:?}", sorted_left_events.iter().collect::<Vec<_>>());
 
@@ -249,7 +249,7 @@ impl StateResolution {
         events_to_sort: &[EventId],
         auth_diff: &HashSet<EventId>,
         fetch_event: F,
-    ) -> Vec<EventId>
+    ) -> Result<Vec<EventId>>
     where
         E: Event,
         F: Fn(&EventId) -> Option<Arc<E>>,
@@ -284,15 +284,15 @@ impl StateResolution {
         }
 
         StateResolution::lexicographical_topological_sort(&graph, |event_id| {
-            let ev = fetch_event(event_id).unwrap();
-            let pl = event_to_pl.get(event_id).unwrap();
+            let ev = fetch_event(event_id).ok_or_else(|| Error::NotFound("".into()))?;
+            let pl = event_to_pl.get(event_id).ok_or_else(|| Error::NotFound("".into()))?;
 
             debug!("{:?}", (-*pl, ev.origin_server_ts(), &ev.event_id()));
 
             // This return value is the key used for sorting events,
             // events are then sorted by power level, time,
             // and lexically by event_id.
-            (-*pl, ev.origin_server_ts(), ev.event_id().clone())
+            Ok((-*pl, ev.origin_server_ts(), ev.event_id().clone()))
         })
     }
 
@@ -302,9 +302,9 @@ impl StateResolution {
     pub fn lexicographical_topological_sort<F>(
         graph: &HashMap<EventId, HashSet<EventId>>,
         key_fn: F,
-    ) -> Vec<EventId>
+    ) -> Result<Vec<EventId>>
     where
-        F: Fn(&EventId) -> (i64, MilliSecondsSinceUnixEpoch, EventId),
+        F: Fn(&EventId) -> Result<(i64, MilliSecondsSinceUnixEpoch, EventId)>,
     {
         info!("starting lexicographical topological sort");
         // NOTE: an event that has no incoming edges happened most recently,
@@ -314,12 +314,12 @@ impl StateResolution {
         // outgoing edges, c.f.
         // https://en.wikipedia.org/wiki/Topological_sorting#Kahn's_algorithm
 
-        // TODO make the HashSet conversion cleaner ??
         // outdegree_map is an event referring to the events before it, the
         // more outdegree's the more recent the event.
         let mut outdegree_map = graph.clone();
 
-        // The number of events that depend on the given event (the eventId key)
+        // The number of events that depend on the given event (the EventId key)
+        // How many events reference this event in the DAG as a parent
         let mut reverse_graph = HashMap::new();
 
         // Vec of nodes that have zero out degree, least recent events.
@@ -329,7 +329,7 @@ impl StateResolution {
             if edges.is_empty() {
                 // The `Reverse` is because rusts `BinaryHeap` sorts largest -> smallest we need
                 // smallest -> largest
-                zero_outdegree.push(Reverse((key_fn(node), node)));
+                zero_outdegree.push(Reverse((key_fn(node)?, node)));
             }
 
             reverse_graph.entry(node).or_insert(hashset![]);
@@ -345,14 +345,17 @@ impl StateResolution {
         // Destructure the `Reverse` and take the smallest `node` each time
         while let Some(Reverse((_, node))) = heap.pop() {
             let node: &EventId = node;
-            for parent in reverse_graph.get(node).unwrap() {
+            for parent in reverse_graph.get(node).expect("EventId in heap is also in reverse_graph")
+            {
                 // The number of outgoing edges this node has
-                let out = outdegree_map.get_mut(parent).unwrap();
+                let out = outdegree_map
+                    .get_mut(parent)
+                    .expect("outdegree_map knows of all referenced EventIds");
 
                 // Only push on the heap once older events have been cleared
                 out.remove(node);
                 if out.is_empty() {
-                    heap.push(Reverse((key_fn(parent), parent)));
+                    heap.push(Reverse((key_fn(parent)?, parent)));
                 }
             }
 
@@ -360,7 +363,7 @@ impl StateResolution {
             sorted.push(node.clone());
         }
 
-        sorted
+        Ok(sorted)
     }
 
     /// Find the power level for the sender of `event_id` or return a default value of zero.
@@ -516,7 +519,7 @@ impl StateResolution {
         to_sort: &[EventId],
         resolved_power_level: Option<&EventId>,
         fetch_event: F,
-    ) -> Vec<EventId>
+    ) -> Result<Vec<EventId>>
     where
         E: Event,
         F: Fn(&EventId) -> Option<Arc<E>>,
@@ -525,7 +528,7 @@ impl StateResolution {
 
         // There are no EventId's to sort, bail.
         if to_sort.is_empty() {
-            return vec![];
+            return Ok(vec![]);
         }
 
         let mut mainline = vec![];
@@ -533,11 +536,13 @@ impl StateResolution {
         while let Some(p) = pl {
             mainline.push(p.clone());
 
-            let event = fetch_event(&p).unwrap();
+            let event =
+                fetch_event(&p).ok_or_else(|| Error::NotFound(format!("Failed to find {}", p)))?;
             let auth_events = &event.auth_events();
             pl = None;
             for aid in auth_events {
-                let ev = fetch_event(aid).unwrap();
+                let ev = fetch_event(aid)
+                    .ok_or_else(|| Error::NotFound(format!("Failed to find {}", aid)))?;
                 if is_type_and_key(&ev, EventType::RoomPowerLevels, "") {
                     pl = Some(aid.clone());
                     break;
@@ -582,7 +587,7 @@ impl StateResolution {
         let mut sort_event_ids = order_map.keys().map(|&k| k.clone()).collect::<Vec<_>>();
         sort_event_ids.sort_by_key(|sort_id| order_map.get(sort_id).unwrap());
 
-        sort_event_ids
+        Ok(sort_event_ids)
     }
 
     /// Get the mainline depth from the `mainline_map` or finds a power_level event
diff --git a/crates/ruma-state-res/tests/event_sorting.rs b/crates/ruma-state-res/tests/event_sorting.rs
index 39ab675a..31d9bc06 100644
--- a/crates/ruma-state-res/tests/event_sorting.rs
+++ b/crates/ruma-state-res/tests/event_sorting.rs
@@ -32,10 +32,9 @@ fn test_event_sort() {
     let sorted_power_events =
         StateResolution::reverse_topological_power_sort(&power_events, &auth_chain, |id| {
             events.get(id).map(Arc::clone)
-        });
+        })
+        .unwrap();
 
-    // This is a TODO in conduit
-    // TODO we may be able to skip this since they are resolved according to spec
     let resolved_power = StateResolution::iterative_auth_check(
         &RoomVersion::version_6(),
         &sorted_power_events,
@@ -53,7 +52,8 @@ fn test_event_sort() {
 
     let sorted_event_ids = StateResolution::mainline_sort(&events_to_sort, power_level, |id| {
         events.get(id).map(Arc::clone)
-    });
+    })
+    .unwrap();
 
     assert_eq!(
         vec![
diff --git a/crates/ruma-state-res/tests/state_res.rs b/crates/ruma-state-res/tests/state_res.rs
index c72873c8..46de5098 100644
--- a/crates/ruma-state-res/tests/state_res.rs
+++ b/crates/ruma-state-res/tests/state_res.rs
@@ -286,8 +286,9 @@ fn test_lexicographical_sort() {
     };
 
     let res = StateResolution::lexicographical_topological_sort(&graph, |id| {
-        (0, MilliSecondsSinceUnixEpoch(uint!(0)), id.clone())
-    });
+        Ok((0, MilliSecondsSinceUnixEpoch(uint!(0)), id.clone()))
+    })
+    .unwrap();
 
     assert_eq!(
         vec!["o", "l", "n", "m", "p"],
diff --git a/crates/ruma-state-res/tests/utils.rs b/crates/ruma-state-res/tests/utils.rs
index ddd20689..5fb12865 100644
--- a/crates/ruma-state-res/tests/utils.rs
+++ b/crates/ruma-state-res/tests/utils.rs
@@ -80,8 +80,10 @@ pub fn do_check(
     // Resolve the current state and add it to the state_at_event map then continue
     // on in "time"
     for node in StateResolution::lexicographical_topological_sort(&graph, |id| {
-        (0, MilliSecondsSinceUnixEpoch(uint!(0)), id.clone())
-    }) {
+        Ok((0, MilliSecondsSinceUnixEpoch(uint!(0)), id.clone()))
+    })
+    .unwrap()
+    {
         let fake_event = fake_event_map.get(&node).unwrap();
         let event_id = fake_event.event_id().clone();