diff --git a/lib/shared/dm-ops/add-members-spec.js b/lib/shared/dm-ops/add-members-spec.js
--- a/lib/shared/dm-ops/add-members-spec.js
+++ b/lib/shared/dm-ops/add-members-spec.js
@@ -76,9 +76,31 @@
       currentThreadInfo.id,
       defaultRoleID,
     );
-    const newMembers = addedUserIDs
-      .filter(userID => !userIsMember(currentThreadInfo, userID))
-      .map(userID =>
+
+    const memberTimestamps = { ...currentThreadInfo.timestamps.members };
+    const newMembers = [];
+    for (const userID of addedUserIDs) {
+      if (!memberTimestamps[userID]) {
+        memberTimestamps[userID] = {
+          isMember: time,
+          subscription: currentThreadInfo.creationTime,
+        };
+      }
+
+      if (memberTimestamps[userID].isMember > time) {
+        continue;
+      }
+
+      memberTimestamps[userID] = {
+        ...memberTimestamps[userID],
+        isMember: time,
+      };
+
+      if (userIsMember(currentThreadInfo, userID)) {
+        continue;
+      }
+
+      newMembers.push(
         minimallyEncodeMemberInfo<ThickMemberInfo>({
           id: userID,
           role: defaultRoleID,
@@ -87,10 +109,15 @@
           subscription: joinThreadSubscription,
         }),
       );
+    }
 
     const resultThreadInfo = {
       ...currentThreadInfo,
       members: [...currentThreadInfo.members, ...newMembers],
+      timestamps: {
+        ...currentThreadInfo.timestamps,
+        members: memberTimestamps,
+      },
     };
     const updateInfos = [
       {