diff --git a/packages/grpc-js/src/subchannel-pool.ts b/packages/grpc-js/src/subchannel-pool.ts
index 1b8651cb..d7bccb22 100644
--- a/packages/grpc-js/src/subchannel-pool.ts
+++ b/packages/grpc-js/src/subchannel-pool.ts
@@ -101,7 +101,7 @@ export class SubchannelPool {
       }, REF_CHECK_INTERVAL);
 
       // Unref because this timer should not keep the event loop running.
-      this.cleanupTimer.unref();
+      this.cleanupTimer.unref && this.cleanupTimer.unref();
     }
   }