diff --git a/subscriber.go b/subscriber.go
index 2026834..44560d7 100644
--- a/subscriber.go
+++ b/subscriber.go
@@ -186,7 +186,9 @@ func (s *subscriber) assigned(_ context.Context, c *kgo.Client, assigned map[str
 				kopts:   s.kopts,
 				opts:    s.opts,
 			}
+			s.Lock()
 			s.consumers[tp{topic, partition}] = pc
+			s.Unlock()
 			go pc.consume()
 		}
 	}