diff --git a/packages/fdc3-agent-proxy/src/channels/DefaultChannelSupport.ts b/packages/fdc3-agent-proxy/src/channels/DefaultChannelSupport.ts
index 2435fd166..ce88e25e4 100644
--- a/packages/fdc3-agent-proxy/src/channels/DefaultChannelSupport.ts
+++ b/packages/fdc3-agent-proxy/src/channels/DefaultChannelSupport.ts
@@ -32,7 +32,7 @@ export class DefaultChannelSupport implements ChannelSupport {
     constructor(messaging: Messaging, channelSelector: ChannelSelector) {
         this.messaging = messaging;
         this.channelSelector = channelSelector
-        this.channelSelector.setChannelChangeCallback((channelId: string) => {
+        this.channelSelector.setChannelChangeCallback((channelId: string | null) => {
             if (channelId == null) {
                 this.leaveUserChannel()
             } else {
diff --git a/packages/fdc3-get-agent/src/ui/DefaultDesktopAgentChannelSelector.ts b/packages/fdc3-get-agent/src/ui/DefaultDesktopAgentChannelSelector.ts
index 618d63764..e4a45ba83 100644
--- a/packages/fdc3-get-agent/src/ui/DefaultDesktopAgentChannelSelector.ts
+++ b/packages/fdc3-get-agent/src/ui/DefaultDesktopAgentChannelSelector.ts
@@ -14,7 +14,7 @@ type IframeChannelSelected = BrowserTypes.IframeChannelSelected
  */
 export class DefaultDesktopAgentChannelSelector extends AbstractUIComponent implements ChannelSelector {
 
-    private callback: ((channelId: string) => void) | null = null
+    private callback: ((channelId: string | null) => void) | null = null
 
     constructor(url: string | null) {
         super(url ?? "https://fdc3.finos.org/webui/channel_selector.html", "FDC3 Channel Selector")
@@ -27,7 +27,7 @@ export class DefaultDesktopAgentChannelSelector extends AbstractUIComponent impl
         port.addEventListener("message", (e) => {
             if (e.data.type == 'iframeChannelSelected') {
                 const choice = e.data as IframeChannelSelected
-                if ((choice.payload.selected) && (this.callback)) {
+                if (this.callback) {
                     this.callback(choice.payload.selected)
                 }
             }
@@ -51,7 +51,7 @@ export class DefaultDesktopAgentChannelSelector extends AbstractUIComponent impl
         } as IframeChannels)
     }
 
-    setChannelChangeCallback(callback: (channelId: string) => void): void {
+    setChannelChangeCallback(callback: (channelId: string | null) => void): void {
         this.callback = callback
     }
 
diff --git a/packages/fdc3-get-agent/src/ui/NullChannelSelector.ts b/packages/fdc3-get-agent/src/ui/NullChannelSelector.ts
index 11dc9cb20..33e61cd72 100644
--- a/packages/fdc3-get-agent/src/ui/NullChannelSelector.ts
+++ b/packages/fdc3-get-agent/src/ui/NullChannelSelector.ts
@@ -13,7 +13,7 @@ export class NullChannelSelector implements ChannelSelector, Connectable {
     updateChannel(_channelId: string | null, _availableChannels: Channel[]): void {
     }
 
-    setChannelChangeCallback(_callback: (channelId: string) => void): void {
+    setChannelChangeCallback(_callback: (channelId: string | null) => void): void {
     }
 
 
diff --git a/packages/fdc3-get-agent/test/step-definitions/channel-selector.steps.ts b/packages/fdc3-get-agent/test/step-definitions/channel-selector.steps.ts
index 97dd30a02..08c2e22b5 100644
--- a/packages/fdc3-get-agent/test/step-definitions/channel-selector.steps.ts
+++ b/packages/fdc3-get-agent/test/step-definitions/channel-selector.steps.ts
@@ -8,7 +8,7 @@ import { CustomWorld } from "../world";
 Given('A Channel Selector in {string} with callback piping to {string}', async function (this: CustomWorld, field: string, cb: string) {
     const cs = new DefaultDesktopAgentChannelSelector(CHANNEL_SELECTOR_URL);
 
-    cs.setChannelChangeCallback((channelId: string) => {
+    cs.setChannelChangeCallback((channelId: string | null) => {
         this.props[cb] = channelId
     })
 
diff --git a/packages/fdc3-standard/src/ui/ChannelSelector.ts b/packages/fdc3-standard/src/ui/ChannelSelector.ts
index 7d509e6c9..61c23b541 100644
--- a/packages/fdc3-standard/src/ui/ChannelSelector.ts
+++ b/packages/fdc3-standard/src/ui/ChannelSelector.ts
@@ -15,6 +15,6 @@ export interface ChannelSelector extends Connectable {
      * Called on initialisation.  The channel selector will invoke the callback after the 
      * channel is changed.
      */
-    setChannelChangeCallback(callback: (channelId: string) => void): void
+    setChannelChangeCallback(callback: (channelId: string | null) => void): void
 
 }
diff --git a/packages/testing/src/agent/index.ts b/packages/testing/src/agent/index.ts
index d58d587fb..e299672d1 100644
--- a/packages/testing/src/agent/index.ts
+++ b/packages/testing/src/agent/index.ts
@@ -59,7 +59,7 @@ export class SimpleChannelSelector implements ChannelSelector {
         this.cw.props['channels'] = availableChannels
     }
 
-    setChannelChangeCallback(_callback: (channelId: string) => void): void {
+    setChannelChangeCallback(_callback: (channelId: string | null) => void): void {
     }
 
     async connect(): Promise<void> {