diff --git a/WebHostLib/misc.py b/WebHostLib/misc.py
index c57a6386..b3088267 100644
--- a/WebHostLib/misc.py
+++ b/WebHostLib/misc.py
@@ -260,7 +260,10 @@ def host_room(room: UUID):
     # indicate that the page should reload to get the assigned port
     should_refresh = ((not room.last_port and now - room.creation_time < datetime.timedelta(seconds=3))
                       or room.last_activity < now - datetime.timedelta(seconds=room.timeout))
-    with db_session:
+
+    if now - room.last_activity > datetime.timedelta(minutes=1):
+        # we only set last_activity if needed, otherwise parallel access on /room will cause an internal server error
+        # due to "pony.orm.core.OptimisticCheckError: Object Room was updated outside of current transaction"
         room.last_activity = now  # will trigger a spinup, if it's not already running
 
     browser_tokens = "Mozilla", "Chrome", "Safari"