diff --git a/lib/diagnostics_channel.js b/lib/diagnostics_channel.js
index b399c1e2f87ad3..dae0e930a395e9 100644
--- a/lib/diagnostics_channel.js
+++ b/lib/diagnostics_channel.js
@@ -136,7 +136,7 @@ class ActiveChannel {
   }
 
   publish(data) {
-    for (let i = 0; i < this._subscribers.length; i++) {
+    for (let i = 0; i < (this._subscribers?.length || 0); i++) {
       try {
         const onMessage = this._subscribers[i];
         onMessage(data, this.name);
diff --git a/test/parallel/test-diagnostics-channel-sync-unsubscribe.js b/test/parallel/test-diagnostics-channel-sync-unsubscribe.js
new file mode 100644
index 00000000000000..87bf44249f5fc4
--- /dev/null
+++ b/test/parallel/test-diagnostics-channel-sync-unsubscribe.js
@@ -0,0 +1,14 @@
+'use strict';
+
+const common = require('../common');
+const dc = require('node:diagnostics_channel');
+
+const channel_name = 'test:channel';
+const published_data = 'some message';
+
+const onMessageHandler = common.mustCall(() => dc.unsubscribe(channel_name, onMessageHandler));
+
+dc.subscribe(channel_name, onMessageHandler);
+
+// This must not throw.
+dc.channel(channel_name).publish(published_data);