diff --git a/src/Monitoring/ThreadWatcher.coffee b/src/Monitoring/ThreadWatcher.coffee
index f7be7a06a..46ce54e8c 100644
--- a/src/Monitoring/ThreadWatcher.coffee
+++ b/src/Monitoring/ThreadWatcher.coffee
@@ -350,11 +350,11 @@ ThreadWatcher =
 
     else if @status is 404
       if SW[software].mayLackJSON and !data.last?
-        ThreadWatcher.db.extend {siteID, boardID, threadID, val: {last: -1}, rm: ['unread', 'quotingYou']}
+        ThreadWatcher.db.extend {siteID, boardID, threadID, val: {last: -1, unread: undefined, quotingYou: undefined}}
       else if Conf['Auto Prune']
         ThreadWatcher.db.delete {siteID, boardID, threadID}
       else
-        ThreadWatcher.db.extend {siteID, boardID, threadID, val: {isDead: true}, rm: ['unread', 'quotingYou']}
+        ThreadWatcher.db.extend {siteID, boardID, threadID, val: {isDead: true, unread: undefined, quotingYou: undefined}}
 
       ThreadWatcher.refresh()
 
@@ -493,7 +493,7 @@ ThreadWatcher =
       ThreadWatcher.db.delete {boardID, threadID}
       return cb()
     return cb() if data.isDead and not (data.unread? or data.quotingYou?)
-    ThreadWatcher.db.extend {boardID, threadID, val: {isDead: true}, rm: ['unread', 'quotingYou']}, cb
+    ThreadWatcher.db.extend {boardID, threadID, val: {isDead: true, unread: undefined, quotingYou: undefined}}, cb
 
   toggle: (thread) ->
     siteID   = Site.hostname
diff --git a/src/classes/DataBoard.coffee b/src/classes/DataBoard.coffee
index dddee55fd..b06d961d9 100644
--- a/src/classes/DataBoard.coffee
+++ b/src/classes/DataBoard.coffee
@@ -85,11 +85,14 @@ class DataBoard
     else
       @data[siteID].boards[boardID] = val
 
-  extend: ({siteID, boardID, threadID, postID, val, rm}, cb) ->
+  extend: ({siteID, boardID, threadID, postID, val}, cb) ->
     @save =>
       oldVal = @get {siteID, boardID, threadID, postID, defaultValue: {}}
-      delete oldVal[key] for key in rm or []
-      $.extend oldVal, val
+      for key, subVal of val
+        if subVal is undefined
+          delete oldVal[key]
+        else
+          oldVal[key] = subVal
       @setUnsafe {siteID, boardID, threadID, postID, val: oldVal}
     , cb