diff --git a/src/services/slack.ts b/src/services/slack.ts
index 6ca5bd8..97dfbcb 100644
--- a/src/services/slack.ts
+++ b/src/services/slack.ts
@@ -56,16 +56,16 @@ export type SlackBlock = {
 }
 
 export type SlackPostMessageParams = {
-  /**
-   * The ID of the channel to send the message to.
-   */
-  channel: string
-
   /**
    * The text of the message to send.
    */
   text: string
 
+  /**
+   * The ID of the channel to send the message to.
+   */
+  channel?: string
+
   /**
    * The timestamp of a parent message to send the message as a reply to.
    */
@@ -165,8 +165,14 @@ export class SlackClient {
    * Sends a message to a channel.
    */
   public async sendMessage(options: SlackPostMessageParams) {
+    if (!options.channel && !this.defaultChannel) {
+      throw new Error('Error: No channel specified')
+    }
     const res = await this.api.post('chat.postMessage', {
-      json: options
+      json: {
+        channel: this.defaultChannel,
+        ...options
+      }
     })
     return res.json<SlackMessage>()
   }
diff --git a/test/slack.test.ts b/test/slack.test.ts
index ab3abf7..1ea7176 100644
--- a/test/slack.test.ts
+++ b/test/slack.test.ts
@@ -5,7 +5,7 @@ import { SlackClient } from '@/services/slack'
 import './_utils'
 
 test('SlackClient.sendMessage', async (t) => {
-  if (!process.env.SLACK_API_KEY) {
+  if (!process.env.SLACK_API_KEY || !process.env.SLACK_DEFAULT_CHANNEL) {
     return t.pass()
   }
 
@@ -13,14 +13,13 @@ test('SlackClient.sendMessage', async (t) => {
   const client = new SlackClient()
 
   const result = await client.sendMessage({
-    text: 'Hello World!',
-    channelId: 'D05B1AHA55L'
+    text: 'Hello World!'
   })
   t.truthy(result)
 })
 
 test('SlackClient.sendAndWaitForReply', async (t) => {
-  if (!process.env.SLACK_API_KEY) {
+  if (!process.env.SLACK_API_KEY || !process.env.SLACK_DEFAULT_CHANNEL) {
     return t.pass()
   }
 
@@ -31,7 +30,6 @@ test('SlackClient.sendAndWaitForReply', async (t) => {
     async () => {
       await client.sendAndWaitForReply({
         text: 'Please reply to this message with "yes" or "no"',
-        channelId: 'D05B1AHA55L',
         validate: () => false, // never validate so we timeout
         timeoutMs: 1000,
         intervalMs: 100