diff --git a/nomad/job_endpoint_hook_expose_check.go b/nomad/job_endpoint_hook_expose_check.go
index ad60f706a466..7b2202438a3e 100644
--- a/nomad/job_endpoint_hook_expose_check.go
+++ b/nomad/job_endpoint_hook_expose_check.go
@@ -24,6 +24,15 @@ func (jobExposeCheckHook) Mutate(job *structs.Job) (_ *structs.Job, warnings []e
 		for _, s := range tg.Services {
 			for _, c := range s.Checks {
 				if c.Expose {
+					// TG isn't validated yet, but validation
+					// may depend on mutation results.
+					// Do basic validation here and skip mutation,
+					// so Validate can return a meaningful error
+					// messages
+					if !s.Connect.HasSidecar() {
+						continue
+					}
+
 					if exposePath, err := exposePathForCheck(tg, s, c); err != nil {
 						return nil, nil, err
 					} else if exposePath != nil {
diff --git a/nomad/job_endpoint_hooks.go b/nomad/job_endpoint_hooks.go
index a7594ea91f76..043367ea0a89 100644
--- a/nomad/job_endpoint_hooks.go
+++ b/nomad/job_endpoint_hooks.go
@@ -40,6 +40,8 @@ type jobValidator interface {
 }
 
 func (j *Job) admissionControllers(job *structs.Job) (out *structs.Job, warnings []error, err error) {
+	// Mutators run first before validators, so validators view the final rendered job.
+	// So, mutators must handle invalid jobs.
 	out, warnings, err = j.admissionMutators(job)
 	if err != nil {
 		return nil, nil, err
diff --git a/nomad/job_endpoint_test.go b/nomad/job_endpoint_test.go
index 62bad2c33eb6..82dace1c4340 100644
--- a/nomad/job_endpoint_test.go
+++ b/nomad/job_endpoint_test.go
@@ -652,6 +652,57 @@ func TestJobEndpoint_Register_ConnectWithSidecarTask(t *testing.T) {
 
 }
 
+func TestJobEndpoint_Register_Connect_ValidatesWithoutSidecarTask(t *testing.T) {
+	t.Parallel()
+
+	s1, cleanupS1 := TestServer(t, func(c *Config) {
+		c.NumSchedulers = 0 // Prevent automatic dequeue
+	})
+	defer cleanupS1()
+	codec := rpcClient(t, s1)
+	testutil.WaitForLeader(t, s1.RPC)
+
+	// Create the register request
+	job := mock.Job()
+	job.TaskGroups[0].Networks = structs.Networks{
+		{
+			Mode: "bridge",
+		},
+	}
+	job.TaskGroups[0].Tasks[0].Services = nil
+	job.TaskGroups[0].Services = []*structs.Service{
+		{
+			Name:      "backend",
+			PortLabel: "8080",
+			Connect: &structs.ConsulConnect{
+				SidecarService: nil,
+			},
+			Checks: []*structs.ServiceCheck{{
+				Name:     "exposed_no_sidecar",
+				Type:     "http",
+				Expose:   true,
+				Path:     "/health",
+				Interval: 10 * time.Second,
+				Timeout:  2 * time.Second,
+			}},
+		},
+	}
+
+	req := &structs.JobRegisterRequest{
+		Job: job,
+		WriteRequest: structs.WriteRequest{
+			Region:    "global",
+			Namespace: job.Namespace,
+		},
+	}
+
+	// Fetch the response
+	var resp structs.JobRegisterResponse
+	err := msgpackrpc.CallWithCodec(codec, "Job.Register", req, &resp)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "exposed_no_sidecar requires use of sidecar_proxy")
+}
+
 // TestJobEndpoint_Register_Connect_AllowUnauthenticatedFalse asserts that a job
 // submission fails allow_unauthenticated is false, and either an invalid or no
 // operator Consul token is provided.