diff --git a/lib/reducers/message-reducer.js b/lib/reducers/message-reducer.js
--- a/lib/reducers/message-reducer.js
+++ b/lib/reducers/message-reducer.js
@@ -126,6 +126,13 @@
   );
 }
 
+const newThread = () => ({
+  messageIDs: [],
+  startReached: false,
+  lastNavigatedTo: 0,
+  lastPruned: Date.now(),
+});
+
 type FreshMessageStoreResult = {
   +messageStoreOperations: $ReadOnlyArray<MessageStoreOperation>,
   +messageStore: MessageStore,
@@ -154,14 +161,12 @@
   const threadsToMessageIDs = mapThreadsToMessageIDsFromOrderedMessageInfos(
     orderedMessageInfos,
   );
-  const lastPruned = Date.now();
   const threads = _mapValuesWithKeys(
     (messageIDs: string[], threadID: string) => ({
+      ...newThread(),
       messageIDs,
       startReached:
         truncationStatus[threadID] === messageTruncationStatus.EXHAUSTIVE,
-      lastNavigatedTo: 0,
-      lastPruned,
     }),
   )(threadsToMessageIDs);
   const watchedIDs = threadWatcher.getWatchedIDs();
@@ -173,12 +178,7 @@
     ) {
       continue;
     }
-    threads[threadID] = {
-      messageIDs: [],
-      startReached: false,
-      lastNavigatedTo: 0,
-      lastPruned,
-    };
+    threads[threadID] = newThread();
   }
   return {
     messageStoreOperations,
@@ -418,7 +418,6 @@
   );
   const oldMessageInfosToCombine = [];
   const threadsThatNeedMessageIDsResorted = [];
-  const lastPruned = Date.now();
   const local = {};
   const threads = _flow(
     _mapValuesWithKeys((messageIDs: string[], threadID: string) => {
@@ -426,10 +425,9 @@
       const truncate = truncationStatus[threadID];
       if (!oldThread) {
         return {
+          ...newThread(),
           messageIDs,
           startReached: truncate === messageTruncationStatus.EXHAUSTIVE,
-          lastNavigatedTo: 0,
-          lastPruned,
         };
       }
       let oldMessageIDsUnchanged = true;
@@ -611,12 +609,7 @@
       isThreadWatched(threadID, threadInfo, watchedIDs) &&
       !filteredThreads[threadID]
     ) {
-      filteredThreads[threadID] = {
-        messageIDs: [],
-        startReached: false,
-        lastNavigatedTo: 0,
-        lastPruned: Date.now(),
-      };
+      filteredThreads[threadID] = newThread();
     }
   }