diff --git a/engine/controller/aggregate/controller.go b/engine/controller/aggregate/controller.go
index 2568cf00..03353ea2 100644
--- a/engine/controller/aggregate/controller.go
+++ b/engine/controller/aggregate/controller.go
@@ -50,6 +50,7 @@ func (c *Controller) Handle(
 		c.Config,
 		"AggregateMessageHandler",
 		"RouteCommandToInstance",
+		c.Config.Handler(),
 		env.Message,
 		func() {
 			id = c.Config.Handler().RouteCommandToInstance(env.Message)
@@ -79,6 +80,7 @@ func (c *Controller) Handle(
 				c.Config,
 				"AggregateRoot",
 				"ApplyEvent",
+				r,
 				env.Message,
 				func() {
 					r.ApplyEvent(env.Message)
@@ -115,6 +117,7 @@ func (c *Controller) Handle(
 		c.Config,
 		"AggregateMessageHandler",
 		"HandleCommand",
+		c.Config.Handler(),
 		env.Message,
 		func() {
 			c.Config.Handler().HandleCommand(r, s, env.Message)
diff --git a/engine/controller/aggregate/scope.go b/engine/controller/aggregate/scope.go
index 5d27d630..e42609e5 100644
--- a/engine/controller/aggregate/scope.go
+++ b/engine/controller/aggregate/scope.go
@@ -76,6 +76,7 @@ func (s *scope) RecordEvent(m dogma.Message) {
 		s.config,
 		"AggregateRoot",
 		"ApplyEvent",
+		s.root,
 		m,
 		func() {
 			s.root.ApplyEvent(m)
diff --git a/engine/controller/integration/controller.go b/engine/controller/integration/controller.go
index 7d84c475..cc223134 100644
--- a/engine/controller/integration/controller.go
+++ b/engine/controller/integration/controller.go
@@ -47,6 +47,7 @@ func (c *Controller) Handle(
 		c.Config,
 		"IntegrationMessageHandler",
 		"TimeoutHint",
+		c.Config.Handler(),
 		env.Message,
 		func() {
 			t = c.Config.Handler().TimeoutHint(env.Message)
@@ -72,6 +73,7 @@ func (c *Controller) Handle(
 		c.Config,
 		"IntegrationMessageHandler",
 		"HandleCommand",
+		c.Config.Handler(),
 		env.Message,
 		func() {
 			err = c.Config.Handler().HandleCommand(ctx, s, env.Message)
diff --git a/engine/controller/process/controller.go b/engine/controller/process/controller.go
index e326f284..c929a8a2 100644
--- a/engine/controller/process/controller.go
+++ b/engine/controller/process/controller.go
@@ -70,6 +70,7 @@ func (c *Controller) Handle(
 		c.Config,
 		"ProcessMessageHandler",
 		"TimeoutHint",
+		c.Config.Handler(),
 		env.Message,
 		func() {
 			t = c.Config.Handler().TimeoutHint(env.Message)
@@ -173,6 +174,7 @@ func (c *Controller) routeEvent(
 		c.Config,
 		"ProcessMessageHandler",
 		"RouteEventToInstance",
+		handler,
 		env.Message,
 		func() {
 			id, ok, err = handler.RouteEventToInstance(ctx, env.Message)
@@ -234,6 +236,7 @@ func (c *Controller) handle(ctx context.Context, s *scope) error {
 		c.Config,
 		"ProcessMessageHandler",
 		method,
+		c.Config.Handler(),
 		s.env.Message,
 		func() {
 			if s.env.Role == message.EventRole {
diff --git a/engine/controller/projection/controller.go b/engine/controller/projection/controller.go
index b667b01e..af40b0d3 100644
--- a/engine/controller/projection/controller.go
+++ b/engine/controller/projection/controller.go
@@ -80,6 +80,7 @@ func (c *Controller) Handle(
 		c.Config,
 		"ProjectionMessageHandler",
 		"TimeoutHint",
+		handler,
 		env.Message,
 		func() {
 			t = handler.TimeoutHint(env.Message)
@@ -149,6 +150,7 @@ func (c *Controller) Handle(
 		c.Config,
 		"ProjectionMessageHandler",
 		"HandleEvent",
+		handler,
 		env.Message,
 		func() {
 			ok, err = handler.HandleEvent(
diff --git a/engine/panicx/unexpectedmessage.go b/engine/panicx/unexpectedmessage.go
index e91b60aa..11833d45 100644
--- a/engine/panicx/unexpectedmessage.go
+++ b/engine/panicx/unexpectedmessage.go
@@ -17,6 +17,9 @@ type UnexpectedMessage struct {
 	// controller called resulting in the panic.
 	Interface string
 
+	// Implementation is the value that implements the nominated interface.
+	Implementation interface{}
+
 	// Method is the name of the method that the controller called resulting in
 	// the panic.
 	Method string
@@ -30,9 +33,10 @@ type UnexpectedMessage struct {
 
 func (x UnexpectedMessage) String() string {
 	return fmt.Sprintf(
-		"the '%s' %s message handler did not expect %s() to be called with a message of type %T",
+		"the '%s' %s message handler did not expect %T.%s() to be called with a message of type %T",
 		x.Handler.Identity().Name,
 		x.Handler.HandlerType(),
+		x.Implementation,
 		x.Method,
 		x.Message,
 	)
@@ -43,7 +47,8 @@ func (x UnexpectedMessage) String() string {
 // the failure.
 func EnrichUnexpectedMessage(
 	h configkit.RichHandler,
-	iface, method string,
+	iface string, method string,
+	impl interface{},
 	m dogma.Message,
 	fn func(),
 ) {
@@ -56,11 +61,12 @@ func EnrichUnexpectedMessage(
 
 		if v == dogma.UnexpectedMessage {
 			v = UnexpectedMessage{
-				Handler:       h,
-				Interface:     iface,
-				Method:        method,
-				Message:       m,
-				PanicLocation: LocationOfPanic(),
+				Handler:        h,
+				Interface:      iface,
+				Method:         method,
+				Implementation: impl,
+				Message:        m,
+				PanicLocation:  LocationOfPanic(),
 			}
 		}
 
diff --git a/engine/panicx/unexpectedmessage_test.go b/engine/panicx/unexpectedmessage_test.go
index ddbd314e..ce24a3ee 100644
--- a/engine/panicx/unexpectedmessage_test.go
+++ b/engine/panicx/unexpectedmessage_test.go
@@ -28,7 +28,7 @@ var _ = Describe("type UnexpectedMessage", func() {
 
 				x := r.(UnexpectedMessage)
 				Expect(x.String()).To(Equal(
-					"the '<name>' projection message handler did not expect <method>() to be called with a message of type fixtures.MessageA",
+					"the '<name>' projection message handler did not expect *fixtures.ProjectionMessageHandler.<method>() to be called with a message of type fixtures.MessageA",
 				))
 			}()
 
@@ -36,6 +36,7 @@ var _ = Describe("type UnexpectedMessage", func() {
 				config,
 				"<interface>",
 				"<method>",
+				config.Handler(),
 				MessageA1,
 				func() {
 					panic(dogma.UnexpectedMessage)
@@ -62,6 +63,7 @@ var _ = Describe("func EnrichUnexpectedMessage()", func() {
 			config,
 			"<interface>",
 			"<method>",
+			config.Handler(),
 			MessageA1,
 			func() {
 				called = true
@@ -77,6 +79,7 @@ var _ = Describe("func EnrichUnexpectedMessage()", func() {
 				config,
 				"<interface>",
 				"<method>",
+				config.Handler(),
 				MessageA1,
 				func() {
 					panic("<panic>")
@@ -91,23 +94,23 @@ var _ = Describe("func EnrichUnexpectedMessage()", func() {
 				config,
 				"<interface>",
 				"<method>",
+				config.Handler(),
 				MessageA1,
-				func() {
-					panic(dogma.UnexpectedMessage)
-				},
+				panicWithUnexpectedMessage,
 			)
 		}).To(PanicWith(
 			MatchAllFields(
 				Fields{
-					"Handler":   Equal(config),
-					"Interface": Equal("<interface>"),
-					"Method":    Equal("<method>"),
-					"Message":   Equal(MessageA1),
+					"Handler":        Equal(config),
+					"Interface":      Equal("<interface>"),
+					"Method":         Equal("<method>"),
+					"Implementation": Equal(config.Handler()),
+					"Message":        Equal(MessageA1),
 					"PanicLocation": MatchAllFields(
 						Fields{
-							"Func": Not(BeEmpty()),
-							"File": HaveSuffix("/unexpectedmessage_test.go"),
-							"Line": Equal(96),
+							"Func": Equal("github.com/dogmatiq/testkit/engine/panicx_test.panicWithUnexpectedMessage"),
+							"File": HaveSuffix("/engine/panicx/unexpectedmessage_test.go"),
+							"Line": Equal(123),
 						},
 					),
 				},
@@ -115,3 +118,7 @@ var _ = Describe("func EnrichUnexpectedMessage()", func() {
 		))
 	})
 })
+
+func panicWithUnexpectedMessage() {
+	panic(dogma.UnexpectedMessage)
+}