diff --git a/lib/pop3/connection.js b/lib/pop3/connection.js
index d03aee95..b1e1f15c 100644
--- a/lib/pop3/connection.js
+++ b/lib/pop3/connection.js
@@ -998,6 +998,12 @@ class POP3Connection extends EventEmitter {
                     username,
                     'PLAIN'
                 );
+
+                if (!this.session) {
+                    // already closed, do nothing
+                    return;
+                }
+                    
                 this.session.user = response.user;
 
                 this.openMailbox(err => {