diff --git a/util/eventbus/bus_test.go b/util/eventbus/bus_test.go
index 7782634ae..67f68cd4a 100644
--- a/util/eventbus/bus_test.go
+++ b/util/eventbus/bus_test.go
@@ -257,8 +257,8 @@ func TestMonitor(t *testing.T) {
 			cli := bus.Client("test client")
 
 			// The monitored goroutine runs until the client or test subscription ends.
+			sub := eventbus.Subscribe[string](cli)
 			m := cli.Monitor(func(c *eventbus.Client) {
-				sub := eventbus.Subscribe[string](cli)
 				select {
 				case <-c.Done():
 					t.Log("client closed")
@@ -294,6 +294,43 @@ func TestMonitor(t *testing.T) {
 	t.Run("Wait", testMon(t, func(c *eventbus.Client, m eventbus.Monitor) { c.Close(); m.Wait() }))
 }
 
+func TestRegression(t *testing.T) {
+	bus := eventbus.New()
+	t.Cleanup(bus.Close)
+
+	t.Run("SubscribeClosed", func(t *testing.T) {
+		c := bus.Client("test sub client")
+		c.Close()
+
+		var v any
+		func() {
+			defer func() { v = recover() }()
+			eventbus.Subscribe[string](c)
+		}()
+		if v == nil {
+			t.Fatal("Expected a panic from Subscribe on a closed client")
+		} else {
+			t.Logf("Got expected panic: %v", v)
+		}
+	})
+
+	t.Run("PublishClosed", func(t *testing.T) {
+		c := bus.Client("test pub client")
+		c.Close()
+
+		var v any
+		func() {
+			defer func() { v = recover() }()
+			eventbus.Publish[string](c)
+		}()
+		if v == nil {
+			t.Fatal("expected a panic from Publish on a closed client")
+		} else {
+			t.Logf("Got expected panic: %v", v)
+		}
+	})
+}
+
 type queueChecker struct {
 	t    *testing.T
 	want []any
diff --git a/util/eventbus/client.go b/util/eventbus/client.go
index 176b6f2bc..9b4119865 100644
--- a/util/eventbus/client.go
+++ b/util/eventbus/client.go
@@ -51,6 +51,8 @@ func (c *Client) Close() {
 	c.stop.Stop()
 }
 
+func (c *Client) isClosed() bool { return c.pub == nil && c.sub == nil }
+
 // Done returns a channel that is closed when [Client.Close] is called.
 // The channel is closed after all the publishers and subscribers governed by
 // the client have been closed.
@@ -83,6 +85,10 @@ func (c *Client) subscribeTypes() []reflect.Type {
 func (c *Client) subscribeState() *subscribeState {
 	c.mu.Lock()
 	defer c.mu.Unlock()
+	return c.subscribeStateLocked()
+}
+
+func (c *Client) subscribeStateLocked() *subscribeState {
 	if c.sub == nil {
 		c.sub = newSubscribeState(c)
 	}
@@ -92,6 +98,9 @@ func (c *Client) subscribeState() *subscribeState {
 func (c *Client) addPublisher(pub publisher) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
+	if c.isClosed() {
+		panic("cannot Publish on a closed client")
+	}
 	c.pub.Add(pub)
 }
 
@@ -117,17 +126,29 @@ func (c *Client) shouldPublish(t reflect.Type) bool {
 	return c.publishDebug.active() || c.bus.shouldPublish(t)
 }
 
-// Subscribe requests delivery of events of type T through the given
-// Queue. Panics if the queue already has a subscriber for T.
+// Subscribe requests delivery of events of type T through the given client.
+// It panics if c already has a subscriber for type T, or if c is closed.
 func Subscribe[T any](c *Client) *Subscriber[T] {
-	r := c.subscribeState()
+	// Hold the client lock throughout the subscription process so that a caller
+	// attempting to subscribe on a closed client will get a useful diagnostic
+	// instead of a random panic from inside the subscriber plumbing.
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	// The caller should not race subscriptions with close, give them a useful
+	// diagnostic at the call site.
+	if c.isClosed() {
+		panic("cannot Subscribe on a closed client")
+	}
+
+	r := c.subscribeStateLocked()
 	s := newSubscriber[T](r)
 	r.addSubscriber(s)
 	return s
 }
 
-// Publish returns a publisher for event type T using the given
-// client.
+// Publish returns a publisher for event type T using the given client.
+// It panics if c is closed.
 func Publish[T any](c *Client) *Publisher[T] {
 	p := newPublisher[T](c)
 	c.addPublisher(p)