diff --git a/archived/aria2_0.7.0.js b/archived/aria2_0.7.0.js
index b450184..ce55f19 100644
--- a/archived/aria2_0.7.0.js
+++ b/archived/aria2_0.7.0.js
@@ -68,13 +68,13 @@ class Aria2 {
         this.socket?.then( (ws) => ws.close() );
     }
     set onmessage (callback) {
-        this.jsonrpc.onmessage = callback;
+        this.jsonrpc.onmessage = typeof callback === 'function' ? callback : null;
     }
     get onmessage () {
         return typeof this.jsonrpc.onmessage === 'function' ? this.jsonrpc.onmessage : null;
     }
     set onclose (callback) {
-        this.jsonrpc.onclose = callback;
+        this.jsonrpc.onclose = typeof callback === 'function' ? callback : null;
     }
     get onclose () {
         return typeof this.jsonrpc.onclose === 'function' ? this.jsonrpc.onclose : null;
diff --git a/aria2.js b/aria2.js
index b450184..ce55f19 100644
--- a/aria2.js
+++ b/aria2.js
@@ -68,13 +68,13 @@ class Aria2 {
         this.socket?.then( (ws) => ws.close() );
     }
     set onmessage (callback) {
-        this.jsonrpc.onmessage = callback;
+        this.jsonrpc.onmessage = typeof callback === 'function' ? callback : null;
     }
     get onmessage () {
         return typeof this.jsonrpc.onmessage === 'function' ? this.jsonrpc.onmessage : null;
     }
     set onclose (callback) {
-        this.jsonrpc.onclose = callback;
+        this.jsonrpc.onclose = typeof callback === 'function' ? callback : null;
     }
     get onclose () {
         return typeof this.jsonrpc.onclose === 'function' ? this.jsonrpc.onclose : null;
diff --git a/aria2ws.js b/aria2ws.js
index 51e77cc..6003e21 100644
--- a/aria2ws.js
+++ b/aria2ws.js
@@ -28,13 +28,13 @@ class Aria2WebSocket {
         this.socket.then( (ws) => ws.close() );
     }
     set onmessage (callback) {
-        this._onmessage = callback;
+        this._onmessage = typeof callback === 'function' ? callback : null;
     }
     get onmessage () {
         return typeof this._onmessage === 'function' ? this._onmessage : null;
     }
     set onclose (callback) {
-        this._onclose = callback;
+        this._onclose = typeof callback === 'function' ? callback : null;
     }
     get onclose () {
         return typeof this._onclose === 'function' ? this._onclose : null;