diff --git a/lib/MessageFactory.js b/lib/MessageFactory.js
index 98bee01..d2fb339 100644
--- a/lib/MessageFactory.js
+++ b/lib/MessageFactory.js
@@ -56,7 +56,7 @@ class MessageFactory {
    * @chainable
    */
   setUserId (userId) {
-    this.user_id = userId;
+    this.user_id = userId.toString();
     return this;
   }
   /**
diff --git a/lib/MessageSet.js b/lib/MessageSet.js
index fa6e497..2ef5f64 100644
--- a/lib/MessageSet.js
+++ b/lib/MessageSet.js
@@ -97,7 +97,7 @@ class MessageSet extends MessageFactory {
    * @chainable
    */
   setUserId (userId) {
-    this.user_id = userId;
+    this.user_id = userId.toString();
     return this;
   }
   /**
diff --git a/lib/MessageSink.js b/lib/MessageSink.js
index 7adffed..7d5fcd3 100644
--- a/lib/MessageSink.js
+++ b/lib/MessageSink.js
@@ -334,12 +334,12 @@ class MessageSink {
    * @chainable
    */
   setUserId (userId) {
-    this.user_id = userId;
+    this.user_id = userId.toString();
     return this;
   }
   /**
    * Sets the instance response_time field to the given number
-   * @function setUserId
+   * @function setResponseTime
    * @param {Number} responseTime - the response time of the agent to the user
    *  message.
    * @chainable