diff --git a/.changelog/9284.txt b/.changelog/9284.txt
new file mode 100644
index 000000000..2b9e08d8f
--- /dev/null
+++ b/.changelog/9284.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+agent: prevent duplicate services and check registrations from being synced to servers.
+```
diff --git a/agent/ae/ae.go b/agent/ae/ae.go
index 3c986b5ac..9b2841cc5 100644
--- a/agent/ae/ae.go
+++ b/agent/ae/ae.go
@@ -3,12 +3,14 @@ package ae
 
 import (
 	"fmt"
-	"github.com/hashicorp/consul/lib"
-	"github.com/hashicorp/consul/logging"
-	"github.com/hashicorp/go-hclog"
 	"math"
 	"sync"
 	"time"
+
+	"github.com/hashicorp/go-hclog"
+
+	"github.com/hashicorp/consul/lib"
+	"github.com/hashicorp/consul/logging"
 )
 
 // scaleThreshold is the number of nodes after which regular sync runs are
@@ -173,8 +175,7 @@ func (s *StateSyncer) nextFSMState(fs fsmState) fsmState {
 			return retryFullSyncState
 		}
 
-		err := s.State.SyncFull()
-		if err != nil {
+		if err := s.State.SyncFull(); err != nil {
 			s.Logger.Error("failed to sync remote state", "error", err)
 			return retryFullSyncState
 		}
diff --git a/agent/local/state.go b/agent/local/state.go
index b4414e910..5851648f9 100644
--- a/agent/local/state.go
+++ b/agent/local/state.go
@@ -11,13 +11,14 @@ import (
 
 	"github.com/armon/go-metrics"
 	"github.com/armon/go-metrics/prometheus"
+	"github.com/hashicorp/go-hclog"
+
 	"github.com/hashicorp/consul/acl"
 	"github.com/hashicorp/consul/agent/structs"
 	"github.com/hashicorp/consul/agent/token"
 	"github.com/hashicorp/consul/api"
 	"github.com/hashicorp/consul/lib"
 	"github.com/hashicorp/consul/types"
-	"github.com/hashicorp/go-hclog"
 )
 
 var StateCounters = []prometheus.CounterDefinition{
@@ -287,7 +288,6 @@ func (l *State) AddServiceWithChecks(service *structs.NodeService, checks []*str
 			return err
 		}
 	}
-
 	return nil
 }
 
@@ -399,12 +399,14 @@ func (l *State) SetServiceState(s *ServiceState) {
 }
 
 func (l *State) setServiceStateLocked(s *ServiceState) {
-	s.WatchCh = make(chan struct{}, 1)
-
 	key := s.Service.CompoundServiceID()
 	old, hasOld := l.services[key]
+	if hasOld {
+		s.InSync = s.Service.IsSame(old.Service)
+	}
 	l.services[key] = s
 
+	s.WatchCh = make(chan struct{}, 1)
 	if hasOld && old.WatchCh != nil {
 		close(old.WatchCh)
 	}
@@ -722,7 +724,13 @@ func (l *State) SetCheckState(c *CheckState) {
 }
 
 func (l *State) setCheckStateLocked(c *CheckState) {
-	l.checks[c.Check.CompoundCheckID()] = c
+	id := c.Check.CompoundCheckID()
+	existing := l.checks[id]
+	if existing != nil {
+		c.InSync = c.Check.IsSame(existing.Check)
+	}
+
+	l.checks[id] = c
 
 	// If this is a check for an aliased service, then notify the waiters.
 	l.notifyIfAliased(c.Check.CompoundServiceID())
@@ -868,8 +876,8 @@ func (l *State) Stats() map[string]string {
 	}
 }
 
-// updateSyncState does a read of the server state, and updates
-// the local sync status as appropriate
+// updateSyncState queries the server for all the services and checks in the catalog
+// registered to this node, and updates the local entries as InSync or Deleted.
 func (l *State) updateSyncState() error {
 	// Get all checks and services from the master
 	req := structs.NodeSpecificRequest{
diff --git a/agent/local/state_test.go b/agent/local/state_test.go
index 4a9b7f8e7..64ccf630f 100644
--- a/agent/local/state_test.go
+++ b/agent/local/state_test.go
@@ -7,8 +7,9 @@ import (
 	"testing"
 	"time"
 
-	"github.com/hashicorp/consul/testrpc"
 	"github.com/hashicorp/go-hclog"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/hashicorp/consul/agent"
 	"github.com/hashicorp/consul/agent/config"
@@ -17,9 +18,8 @@ import (
 	"github.com/hashicorp/consul/agent/token"
 	"github.com/hashicorp/consul/api"
 	"github.com/hashicorp/consul/sdk/testutil/retry"
+	"github.com/hashicorp/consul/testrpc"
 	"github.com/hashicorp/consul/types"
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 )
 
 func unNilMap(in map[string]string) map[string]string {
@@ -28,6 +28,7 @@ func unNilMap(in map[string]string) map[string]string {
 	}
 	return in
 }
+
 func TestAgentAntiEntropy_Services(t *testing.T) {
 	t.Parallel()
 	a := agent.NewTestAgent(t, "")
@@ -2195,3 +2196,52 @@ func drainCh(ch chan struct{}) {
 		}
 	}
 }
+
+func TestState_SyncChanges_DuplicateAddServiceOnlySyncsOnce(t *testing.T) {
+	state := local.NewState(local.Config{}, hclog.New(nil), new(token.Store))
+	rpc := &fakeRPC{}
+	state.Delegate = rpc
+	state.TriggerSyncChanges = func() {}
+
+	srv := &structs.NodeService{
+		Kind:           structs.ServiceKindTypical,
+		ID:             "the-service-id",
+		Service:        "web",
+		EnterpriseMeta: *structs.DefaultEnterpriseMeta(),
+	}
+	checks := []*structs.HealthCheck{
+		{Node: "this-node", CheckID: "the-id-1", Name: "check-healthy-1"},
+		{Node: "this-node", CheckID: "the-id-2", Name: "check-healthy-2"},
+	}
+	tok := "the-token"
+	err := state.AddServiceWithChecks(srv, checks, tok)
+	require.NoError(t, err)
+	require.NoError(t, state.SyncChanges())
+	// 4 rpc calls, one node register, one service register, two checks
+	require.Len(t, rpc.calls, 4)
+
+	// adding the service again should not catalog register
+	err = state.AddServiceWithChecks(srv, checks, tok)
+	require.NoError(t, err)
+	require.NoError(t, state.SyncChanges())
+	require.Len(t, rpc.calls, 4)
+}
+
+type fakeRPC struct {
+	calls []callRPC
+}
+
+type callRPC struct {
+	method string
+	args   interface{}
+	reply  interface{}
+}
+
+func (f *fakeRPC) RPC(method string, args interface{}, reply interface{}) error {
+	f.calls = append(f.calls, callRPC{method: method, args: args, reply: reply})
+	return nil
+}
+
+func (f *fakeRPC) ResolveTokenToIdentity(_ string) (structs.ACLIdentity, error) {
+	return nil, nil
+}