diff --git a/core/appmodule/module.go b/core/appmodule/module.go
index 70ba46b0b4..2502d25c48 100644
--- a/core/appmodule/module.go
+++ b/core/appmodule/module.go
@@ -1,6 +1,9 @@
 package appmodule
 
-import "cosmossdk.io/depinject"
+import (
+	"cosmossdk.io/depinject"
+	"google.golang.org/grpc"
+)
 
 // AppModule is a tag interface for app module implementations to use as a basis
 // for extension interfaces. It provides no functionality itself, but is the
@@ -12,3 +15,23 @@ type AppModule interface {
 	// IsAppModule is a dummy method to tag a struct as implementing an AppModule.
 	IsAppModule()
 }
+
+// HasServices is the extension interface that modules should implement to register
+// implementations of services defined in .proto files.
+type HasServices interface {
+	AppModule
+
+	// RegisterServices registers the module's services with the app's service
+	// registrar.
+	//
+	// Two types of services are currently supported:
+	// - read-only gRPC query services, which are the default.
+	// - transaction message services, which must have the protobuf service
+	//   option "cosmos.msg.v1.service" (defined in "cosmos/msg/v1/service.proto")
+	//   set to true.
+	//
+	// The service registrar will figure out which type of service you are
+	// implementing based on the presence (or absence) of protobuf options. You
+	// do not need to specify this in golang code.
+	RegisterServices(grpc.ServiceRegistrar)
+}