diff --git a/alts/src/main/java/io/grpc/alts/internal/AltsProtocolNegotiator.java b/alts/src/main/java/io/grpc/alts/internal/AltsProtocolNegotiator.java
index 53749f3e1dd0..417dd257798f 100644
--- a/alts/src/main/java/io/grpc/alts/internal/AltsProtocolNegotiator.java
+++ b/alts/src/main/java/io/grpc/alts/internal/AltsProtocolNegotiator.java
@@ -298,6 +298,7 @@ synchronized Channel get() {
     synchronized void close() {
       if (channel != null) {
         channelPool.returnObject(channel);
+        channel = null;
       }
     }
   }