diff --git a/tests/30rooms/13guestaccess.pl b/tests/30rooms/13guestaccess.pl
index f5480bc35..2ea6dd1b0 100644
--- a/tests/30rooms/13guestaccess.pl
+++ b/tests/30rooms/13guestaccess.pl
@@ -34,7 +34,11 @@
 
       matrix_set_room_guest_access( $user, $room_id, "can_join" )
       ->then( sub {
-         matrix_join_room( $guest_user, $room_id )
+         # we use join_room_synced as a proxy for ensuring that the join event
+         # has propagated to the workers, otherwise the worker that receives
+         # the event send request might not know that we are in the room.
+         # (see https://github.com/matrix-org/sytest/issues/836)
+         matrix_join_room_synced( $guest_user, $room_id );
       })->then( sub {
          matrix_send_room_text_message( $guest_user, $room_id, body => "sup" );
       })->then( sub {
@@ -125,7 +129,7 @@
 
       matrix_set_room_guest_access( $user, $room_id, "can_join" )
       ->then( sub {
-         matrix_join_room( $guest_user, $room_id );
+         matrix_join_room_synced( $guest_user, $room_id );
       })->then( sub {
          matrix_get_room_membership( $user, $room_id, $guest_user );
       })->then( sub {
@@ -154,7 +158,11 @@
       my $displayname_uri = "/r0/profile/:user_id/displayname";
 
       matrix_set_room_guest_access( $user, $room_id, "can_join" )->then( sub {
-         matrix_join_room( $guest_user, $room_id );
+         # we use join_room_synced as a proxy for ensuring that the join event
+         # has propagated to the workers, otherwise the worker that receives
+         # the profile request might not know that we are in the room.
+         # (see https://github.com/matrix-org/sytest/issues/836)
+         matrix_join_room_synced( $guest_user, $room_id );
       })->then( sub {
          do_request_json_for( $guest_user,
             method => "GET",
@@ -225,7 +233,7 @@
          })->then( sub {
             matrix_join_room( $remote_user, $room_id );
          })->then( sub {
-            matrix_join_room( $guest_user, $room_id );
+            matrix_join_room_synced( $guest_user, $room_id );
          })->then( sub {
             matrix_get_room_membership( $local_user, $room_id, $guest_user );
          })->then( sub {