diff --git a/CHANGELOG.md b/CHANGELOG.md
index a61ebc4..b7a5ba0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,10 @@
 # Change Log
 
-## v1.2.0 – 2020-06-26
+## v1.2.1 – 2020-06-27
+
+* Fix issue where Slack timestamp format not permitted for `ts` and `threadTs` parameters of the `Message` surface object.
+
+## v1.2.0 – 2020-06-27
 
 * Parameter `ts` for the `Message` surface object is now supported.
 
diff --git a/package.json b/package.json
index e6359b0..3bde273 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "slack-block-builder",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "description": "Maintainable code for interactive Slack messages, modals and home tabs. A must-have for the Slack Block Kit framework.",
   "author": {
     "name": "Ray East",
diff --git a/src/surfaces/message.js b/src/surfaces/message.js
index f87480c..3e89278 100644
--- a/src/surfaces/message.js
+++ b/src/surfaces/message.js
@@ -80,12 +80,12 @@ class Message extends Surface {
    *
    * {@link https://api.slack.com/messaging/composing|View in Slack API Documentation}
    *
-   * @param {timestamp} timestamp The timestamp of message to be replied to
+   * @param {string} string The Slack-produced timestamp of message to be replied to
    * @return {this} The instance on which the method is called
    */
 
-  threadTs(timestamp) {
-    return this.set(timestamp, props.threadTs);
+  threadTs(string) {
+    return this.set(string, props.threadTs);
   }
 
   /**
@@ -93,12 +93,12 @@ class Message extends Surface {
    *
    * {@link https://api.slack.com/messaging/composing|View in Slack API Documentation}
    *
-   * @param {timestamp} timestamp The timestamp of message to be replied to
+   * @param {string} string The Slack-produced timestamp of message to be replaced
    * @return {this} The instance on which the method is called
    */
 
-  ts(timestamp) {
-    return this.set(timestamp, props.ts);
+  ts(string) {
+    return this.set(string, props.ts);
   }
 
   /**
diff --git a/src/utility/validators/default-type-rules.js b/src/utility/validators/default-type-rules.js
index 9822e2d..0d76adf 100644
--- a/src/utility/validators/default-type-rules.js
+++ b/src/utility/validators/default-type-rules.js
@@ -56,8 +56,8 @@ module.exports = {
   notifyOnClose: types.isBool,
   description: types.isString,
   asUser: types.isBool,
-  ts: types.isTimestamp,
-  threadTs: types.isTimestamp,
+  ts: types.isString,
+  threadTs: types.isString,
   replaceOriginal: types.isBool,
   deleteOriginal: types.isBool,
   responseType: types.isResponseTypeEnum,
diff --git a/tests/mocks/valid-prop-data-mapping.js b/tests/mocks/valid-prop-data-mapping.js
index d3fa6f8..de10b56 100644
--- a/tests/mocks/valid-prop-data-mapping.js
+++ b/tests/mocks/valid-prop-data-mapping.js
@@ -55,8 +55,8 @@ module.exports = {
   privateMetaData: types.string,
   callbackId: types.string,
   asUser: types.bool,
-  threadsTs: types.timestamp,
-  ts: types.timestamp,
+  threadsTs: types.string,
+  ts: types.string,
   replaceOriginal: types.bool,
   deleteOriginal: types.bool,
   responseType: types.ephemeral,
diff --git a/tests/surfaces/mocks/message.mock.js b/tests/surfaces/mocks/message.mock.js
index 0e1c89b..8f69dc3 100644
--- a/tests/surfaces/mocks/message.mock.js
+++ b/tests/surfaces/mocks/message.mock.js
@@ -3,9 +3,9 @@ const { getSurfaces, ...Surfaces } = require('../../../src/surfaces');
 const props = {
   channel: 'channel',
   text: 'text',
-  ts: 1593125546.000100,
-  threadTs: 1593125546.000100,
-  postAt: 1593125546.000100,
+  ts: '1593125546.000100',
+  threadTs: '1593125546.000100',
+  postAt: 1593125546,
 };
 
 const mock = new Surfaces.Message({ ...props });