diff --git a/app/soapbox/entity-store/__tests__/reducer.test.ts b/app/soapbox/entity-store/__tests__/reducer.test.ts
new file mode 100644
index 0000000000..0da25f25e5
--- /dev/null
+++ b/app/soapbox/entity-store/__tests__/reducer.test.ts
@@ -0,0 +1,79 @@
+import { entitiesFetchFail, entitiesFetchRequest, importEntities } from '../actions';
+import reducer from '../reducer';
+
+import type { EntityCache } from '../types';
+
+interface TestEntity {
+  id: string
+  msg: string
+}
+
+test('import entities', () => {
+  const entities: TestEntity[] = [
+    { id: '1', msg: 'yolo' },
+    { id: '2', msg: 'benis' },
+    { id: '3', msg: 'boop' },
+  ];
+
+  const action = importEntities(entities, 'TestEntity');
+  const result = reducer(undefined, action);
+  const cache = result.TestEntity as EntityCache<TestEntity>;
+
+  expect(cache.store['1']!.msg).toBe('yolo');
+  expect(Object.values(cache.lists).length).toBe(0);
+});
+
+test('import entities into a list', () => {
+  const entities: TestEntity[] = [
+    { id: '1', msg: 'yolo' },
+    { id: '2', msg: 'benis' },
+    { id: '3', msg: 'boop' },
+  ];
+
+  const action = importEntities(entities, 'TestEntity', 'thingies');
+  const result = reducer(undefined, action);
+  const cache = result.TestEntity as EntityCache<TestEntity>;
+
+  expect(cache.store['2']!.msg).toBe('benis');
+  expect(cache.lists.thingies?.ids.size).toBe(3);
+
+  // Now try adding an additional item.
+  const entities2: TestEntity[] = [
+    { id: '4', msg: 'hehe' },
+  ];
+
+  const action2 = importEntities(entities2, 'TestEntity', 'thingies');
+  const result2 = reducer(result, action2);
+  const cache2 = result2.TestEntity as EntityCache<TestEntity>;
+
+  expect(cache2.store['4']!.msg).toBe('hehe');
+  expect(cache2.lists.thingies?.ids.size).toBe(4);
+
+  // Finally, update an item.
+  const entities3: TestEntity[] = [
+    { id: '2', msg: 'yolofam' },
+  ];
+
+  const action3 = importEntities(entities3, 'TestEntity', 'thingies');
+  const result3 = reducer(result2, action3);
+  const cache3 = result3.TestEntity as EntityCache<TestEntity>;
+
+  expect(cache3.store['2']!.msg).toBe('yolofam');
+  expect(cache3.lists.thingies?.ids.size).toBe(4); // unchanged
+});
+
+test('fetching updates the list state', () => {
+  const action = entitiesFetchRequest('TestEntity', 'thingies');
+  const result = reducer(undefined, action);
+
+  expect(result.TestEntity!.lists.thingies!.state.fetching).toBe(true);
+});
+
+test('failure adds the error to the state', () => {
+  const error = new Error('whoopsie');
+
+  const action = entitiesFetchFail('TestEntity', 'thingies', error);
+  const result = reducer(undefined, action);
+
+  expect(result.TestEntity!.lists.thingies!.state.error).toBe(error);
+});
\ No newline at end of file
diff --git a/app/soapbox/entity-store/reducer.ts b/app/soapbox/entity-store/reducer.ts
index f2af680a18..bb1dcdd1d7 100644
--- a/app/soapbox/entity-store/reducer.ts
+++ b/app/soapbox/entity-store/reducer.ts
@@ -48,6 +48,7 @@ const setFetching = (
   entityType: string,
   listKey: string | undefined,
   isFetching: boolean,
+  error?: any,
 ) => {
   return produce(state, draft => {
     const cache = draft[entityType] ?? createCache();
@@ -55,6 +56,7 @@ const setFetching = (
     if (typeof listKey === 'string') {
       const list = cache.lists[listKey] ?? createList();
       list.state.fetching = isFetching;
+      list.state.error = error;
       cache.lists[listKey] = list;
     }
 
@@ -72,7 +74,7 @@ function reducer(state: Readonly<State> = {}, action: EntityAction): State {
     case ENTITIES_FETCH_REQUEST:
       return setFetching(state, action.entityType, action.listKey, true);
     case ENTITIES_FETCH_FAIL:
-      return setFetching(state, action.entityType, action.listKey, false);
+      return setFetching(state, action.entityType, action.listKey, false, action.error);
     default:
       return state;
   }
diff --git a/app/soapbox/entity-store/types.ts b/app/soapbox/entity-store/types.ts
index efec97df13..eb2a306a09 100644
--- a/app/soapbox/entity-store/types.ts
+++ b/app/soapbox/entity-store/types.ts
@@ -5,8 +5,8 @@ interface Entity {
 }
 
 /** Store of entities by ID. */
-interface EntityStore {
-  [id: string]: Entity | undefined
+interface EntityStore<TEntity extends Entity = Entity> {
+  [id: string]: TEntity | undefined
 }
 
 /** List of entity IDs and fetch state. */
@@ -32,9 +32,9 @@ interface EntityListState {
 }
 
 /** Cache data pertaining to a paritcular entity type.. */
-interface EntityCache {
+interface EntityCache<TEntity extends Entity = Entity> {
   /** Map of entities of this type. */
-  store: EntityStore
+  store: EntityStore<TEntity>
   /** Lists of entity IDs for a particular purpose. */
   lists: {
     [listKey: string]: EntityList | undefined