diff --git a/keyserver/src/responders/message-responders.js b/keyserver/src/responders/message-responders.js
--- a/keyserver/src/responders/message-responders.js
+++ b/keyserver/src/responders/message-responders.js
@@ -189,12 +189,13 @@
   );
 
   if (request.mediaIDs) {
-    await assignMedia(viewer, request.mediaIDs, id);
+    await assignMedia(viewer, request.mediaIDs, id, threadID);
   } else {
     await assignMessageContainerToMedia(
       viewer,
       request.mediaMessageContents,
       id,
+      threadID,
     );
   }
 
diff --git a/keyserver/src/updaters/upload-updaters.js b/keyserver/src/updaters/upload-updaters.js
--- a/keyserver/src/updaters/upload-updaters.js
+++ b/keyserver/src/updaters/upload-updaters.js
@@ -10,11 +10,13 @@
   viewer: Viewer,
   mediaIDs: $ReadOnlyArray<string>,
   containerID: string,
+  threadID: string,
 ): Promise<void> {
   const query = SQL`
     UPDATE uploads
-    SET container = ${containerID}
-    WHERE id IN (${mediaIDs}) AND uploader = ${viewer.id} AND container IS NULL
+    SET container = ${containerID}, thread = ${threadID}
+    WHERE id IN (${mediaIDs}) AND uploader = ${viewer.id} 
+      AND container IS NULL AND thread IS NULL
   `;
   await dbQuery(query);
 }
@@ -23,13 +25,15 @@
   viewer: Viewer,
   mediaMessageContents: $ReadOnlyArray<MediaMessageServerDBContent>,
   containerID: string,
+  threadID: string,
 ): Promise<void> {
   const uploadIDs =
     getUploadIDsFromMediaMessageServerDBContents(mediaMessageContents);
   const query = SQL`
     UPDATE uploads
-    SET container = ${containerID}
-    WHERE id IN (${uploadIDs}) AND uploader = ${viewer.id} AND container IS NULL
+    SET container = ${containerID}, thread = ${threadID}
+    WHERE id IN (${uploadIDs}) AND uploader = ${viewer.id} 
+      AND container IS NULL AND thread IS NULL
   `;
   await dbQuery(query);
 }