diff --git a/graal-nodejs/lib/internal/js_stream_socket.js b/graal-nodejs/lib/internal/js_stream_socket.js
index 68e1802a63b..70d6d03069f 100644
--- a/graal-nodejs/lib/internal/js_stream_socket.js
+++ b/graal-nodejs/lib/internal/js_stream_socket.js
@@ -149,6 +149,7 @@ class JSStreamSocket extends Socket {
     }
 
     const handle = this._handle;
+    assert(handle !== null);
 
     process.nextTick(() => {
       // Ensure that write is dispatched asynchronously.
@@ -181,6 +182,8 @@ class JSStreamSocket extends Socket {
     }
 
     const handle = this._handle;
+    assert(handle !== null);
+
     const self = this;
 
     let pending = bufs.length;