diff --git a/lib/reducers/thread-activity-reducer.test.js b/lib/reducers/thread-activity-reducer.test.js
index 0488872d7..03dde0c6d 100644
--- a/lib/reducers/thread-activity-reducer.test.js
+++ b/lib/reducers/thread-activity-reducer.test.js
@@ -1,111 +1,147 @@
 // @flow
 
 import { reduceThreadActivity } from './thread-activity-reducer.js';
+import { messageStorePruneActionType } from '../actions/message-actions.js';
 import { deleteKeyserverAccountActionTypes } from '../actions/user-actions.js';
 import { updateThreadLastNavigatedActionType } from '../types/thread-activity-types.js';
 
 // NOTE: These unit tests were generated by GitHub Copilot.
 
 describe('reduceThreadActivity', () => {
   test('updates the lastNavigatedTo time for a thread', () => {
     const initialState = {
       thread1: {
         lastNavigatedTo: 1639522314170,
         lastPruned: 1639522314170,
       },
       thread2: {
         lastNavigatedTo: 1639522314170,
         lastPruned: 1639522314170,
       },
     };
     const action = {
       type: updateThreadLastNavigatedActionType,
       payload: {
         threadID: 'thread1',
         time: 1639522317443,
       },
     };
     const expectedState = {
       thread1: {
         lastNavigatedTo: 1639522317443,
         lastPruned: 1639522314170,
       },
       thread2: {
         lastNavigatedTo: 1639522314170,
         lastPruned: 1639522314170,
       },
     };
     const result = reduceThreadActivity(initialState, action);
     expect(result).toEqual(expectedState);
   });
 
+  test('should create new thread activity entry with only lastNavigatedTo field', () => {
+    const initialState = {};
+    const action = {
+      type: updateThreadLastNavigatedActionType,
+      payload: {
+        threadID: 'thread1',
+        time: 1639522317443,
+      },
+    };
+    const expectedState = {
+      thread1: {
+        lastNavigatedTo: 1639522317443,
+      },
+    };
+    const result = reduceThreadActivity(initialState, action);
+    expect(result).toEqual(expectedState);
+  });
+
+  test('should create new thread activity entry with only lastPruned field', () => {
+    const initialState = {};
+    const action = {
+      type: messageStorePruneActionType,
+      payload: {
+        threadIDs: ['thread1'],
+      },
+    };
+    const expectedState = {
+      thread1: {
+        lastPruned: expect.any(Number),
+      },
+    };
+    const result = reduceThreadActivity(initialState, action);
+    expect(result).toEqual(expectedState);
+  });
+
   test('returns the initial state if the action type is not recognized', () => {
     const initialState = {
       thread1: {
         lastNavigatedTo: 1639522314170,
         lastPruned: 1639522314170,
       },
       thread2: {
         lastNavigatedTo: 1639522314170,
         lastPruned: 1639522314170,
       },
     };
     const action = {
       type: 'UPDATE_REPORTS_ENABLED',
       payload: {},
     };
     const expectedState = {
       thread1: {
         lastNavigatedTo: 1639522314170,
         lastPruned: 1639522314170,
       },
       thread2: {
         lastNavigatedTo: 1639522314170,
         lastPruned: 1639522314170,
       },
     };
     const result = reduceThreadActivity(initialState, action);
     expect(result).toEqual(expectedState);
   });
 
   test('removes threads of keyserver the user has disconnected from', () => {
     const keyserver1 = '100';
     const keyserver2 = '200';
     const keyserver3 = '300';
     const threads1 = {
       [keyserver1 + '|1']: { lastNavigatedTo: 1, lastPruned: 1 },
       [keyserver1 + '|2']: { lastNavigatedTo: 1, lastPruned: 1 },
     };
     const threads2 = {
       [keyserver2 + '|1']: { lastNavigatedTo: 1, lastPruned: 1 },
       [keyserver2 + '|2']: { lastNavigatedTo: 1, lastPruned: 1 },
     };
     const threads3 = {
       [keyserver3 + '|1']: { lastNavigatedTo: 1, lastPruned: 1 },
       [keyserver3 + '|2']: { lastNavigatedTo: 1, lastPruned: 1 },
     };
 
     const threads = { ...threads1, ...threads2, ...threads3 };
     const action = {
       type: deleteKeyserverAccountActionTypes.success,
       payload: {
         currentUserInfo: { anonymous: true },
         preRequestUserState: {
           cookiesAndSessions: {},
           currentUserInfo: {
             id: '83810',
             username: 'user1',
           },
         },
         keyserverIDs: [keyserver1, keyserver2],
       },
       loadingInfo: {
         fetchIndex: 1,
         trackMultipleRequests: false,
         customKeyName: undefined,
       },
     };
 
     expect(reduceThreadActivity(threads, action)).toEqual(threads3);
   });
 });
diff --git a/lib/types/thread-activity-types.js b/lib/types/thread-activity-types.js
index 21d95b296..b9eacb26e 100644
--- a/lib/types/thread-activity-types.js
+++ b/lib/types/thread-activity-types.js
@@ -1,12 +1,18 @@
 // @flow
 
 export const updateThreadLastNavigatedActionType =
   'UPDATE_THREAD_LAST_NAVIGATED';
 
-export type ThreadActivityStoreEntry = {
-  +lastNavigatedTo: number, // millisecond timestamp
-  +lastPruned: number, // millisecond timestamp
-};
+export type ThreadActivityStoreEntry =
+  | {
+      +lastNavigatedTo: number, // millisecond timestamp
+      +lastPruned?: number, // millisecond timestamp
+    }
+  | {
+      +lastNavigatedTo?: number,
+      +lastPruned: number,
+    };
+
 export type ThreadActivityStore = {
   +[threadID: string]: ThreadActivityStoreEntry,
 };