diff --git a/packages/automerge-repo-network-messagechannel/src/MessagePortRef.ts b/packages/automerge-repo-network-messagechannel/src/MessagePortRef.ts
index 3ea3cf09..b6a409f6 100644
--- a/packages/automerge-repo-network-messagechannel/src/MessagePortRef.ts
+++ b/packages/automerge-repo-network-messagechannel/src/MessagePortRef.ts
@@ -7,6 +7,7 @@ export interface PortRefEvents {
 
 export interface MessagePortRef extends EventEmitter<PortRefEvents> {
   start(): void
+  stop(): void
   postMessage(message: any, transferable?: Transferable[]): void
   isAlive(): boolean
 }
diff --git a/packages/automerge-repo-network-messagechannel/src/StrongMessagePortRef.ts b/packages/automerge-repo-network-messagechannel/src/StrongMessagePortRef.ts
index 87f7524d..5d28779c 100644
--- a/packages/automerge-repo-network-messagechannel/src/StrongMessagePortRef.ts
+++ b/packages/automerge-repo-network-messagechannel/src/StrongMessagePortRef.ts
@@ -5,22 +5,33 @@ export class StrongMessagePortRef
   extends EventEmitter<PortRefEvents>
   implements MessagePortRef
 {
+  isDisconnected: boolean = false
+
   constructor(private port: MessagePort) {
     port.addEventListener("message", event => {
-      this.emit("message", event)
+      if (!this.isDisconnected) {
+        this.emit("message", event)
+      }
     })
 
     super()
   }
 
   postMessage(message: any, transfer: Transferable[]): void {
-    this.port.postMessage(message, transfer)
+    if (!this.isDisconnected) {
+      this.port.postMessage(message, transfer)
+    }
   }
 
   start(): void {
+    this.isDisconnected = false
     this.port.start()
   }
 
+  stop() {
+    this.isDisconnected = true
+  }
+
   isAlive(): boolean {
     /* c8 ignore next */
     return true
diff --git a/packages/automerge-repo-network-messagechannel/src/WeakMessagePortRef.ts b/packages/automerge-repo-network-messagechannel/src/WeakMessagePortRef.ts
index f173a630..bc33e3f6 100644
--- a/packages/automerge-repo-network-messagechannel/src/WeakMessagePortRef.ts
+++ b/packages/automerge-repo-network-messagechannel/src/WeakMessagePortRef.ts
@@ -15,7 +15,9 @@ export class WeakMessagePortRef
     this.weakRef = new WeakRef<MessagePort>(port)
 
     port.addEventListener("message", event => {
-      this.emit("message", event)
+      if (!this.isDisconnected) {
+        this.emit("message", event)
+      }
     })
   }
 
@@ -27,6 +29,10 @@ export class WeakMessagePortRef
       return
     }
 
+    if (this.isDisconnected) {
+      return
+    }
+
     try {
       port.postMessage(message, transfer)
     } catch (err) {
@@ -42,6 +48,8 @@ export class WeakMessagePortRef
       return
     }
 
+    this.isDisconnected = false
+
     try {
       port.start()
     } catch (err) {
@@ -49,6 +57,10 @@ export class WeakMessagePortRef
     }
   }
 
+  stop() {
+    this.isDisconnected = true
+  }
+
   private disconnnect() {
     if (!this.isDisconnected) {
       this.emit("close")
diff --git a/packages/automerge-repo-network-messagechannel/src/index.ts b/packages/automerge-repo-network-messagechannel/src/index.ts
index 4b2b5adc..e3549b19 100644
--- a/packages/automerge-repo-network-messagechannel/src/index.ts
+++ b/packages/automerge-repo-network-messagechannel/src/index.ts
@@ -62,6 +62,7 @@ export class MessageChannelNetworkAdapter extends NetworkAdapter {
     log("messageport connecting")
     this.peerId = peerId
     this.peerMetadata = peerMetadata
+
     this.messagePortRef.start()
     this.messagePortRef.addListener(
       "message",
@@ -153,8 +154,7 @@ export class MessageChannelNetworkAdapter extends NetworkAdapter {
   }
 
   disconnect() {
-    // TODO
-    throw new Error("Unimplemented: leave on MessagePortNetworkAdapter")
+    this.messagePortRef.stop()
   }
 }