diff --git a/agent/agent_endpoint.go b/agent/agent_endpoint.go
index 8d7728f1c..75d5807c0 100644
--- a/agent/agent_endpoint.go
+++ b/agent/agent_endpoint.go
@@ -554,6 +554,14 @@ func (s *HTTPServer) AgentRegisterService(resp http.ResponseWriter, req *http.Re
 		return nil, nil
 	}
 
+	// Run validation. This is the same validation that would happen on
+	// the catalog endpoint so it helps ensure the sync will work properly.
+	if err := ns.Validate(); err != nil {
+		resp.WriteHeader(http.StatusBadRequest)
+		fmt.Fprintf(resp, err.Error())
+		return nil, nil
+	}
+
 	// Verify the check type.
 	chkTypes, err := args.CheckTypes()
 	if err != nil {
diff --git a/agent/agent_endpoint_test.go b/agent/agent_endpoint_test.go
index e30323007..05e8b6ca3 100644
--- a/agent/agent_endpoint_test.go
+++ b/agent/agent_endpoint_test.go
@@ -1398,6 +1398,35 @@ func TestAgent_RegisterService_ConnectProxy(t *testing.T) {
 	assert.Equal("abc123", a.State.ServiceToken("connect-proxy"))
 }
 
+func TestAgent_RegisterService_ConnectProxyInvalid(t *testing.T) {
+	t.Parallel()
+
+	assert := assert.New(t)
+	a := NewTestAgent(t.Name(), "")
+	defer a.Shutdown()
+
+	args := &structs.ServiceDefinition{
+		Kind:             structs.ServiceKindConnectProxy,
+		Name:             "connect-proxy",
+		ProxyDestination: "db",
+		Check: structs.CheckType{
+			TTL: 15 * time.Second,
+		},
+	}
+
+	req, _ := http.NewRequest("PUT", "/v1/agent/service/register?token=abc123", jsonReader(args))
+	resp := httptest.NewRecorder()
+	obj, err := a.srv.AgentRegisterService(resp, req)
+	assert.Nil(err)
+	assert.Nil(obj)
+	assert.Equal(http.StatusBadRequest, resp.Code)
+	assert.Contains(resp.Body.String(), "Port")
+
+	// Ensure the service doesn't exist
+	_, ok := a.State.Services()["connect-proxy"]
+	assert.False(ok)
+}
+
 func TestAgent_DeregisterService(t *testing.T) {
 	t.Parallel()
 	a := NewTestAgent(t.Name(), "")