diff --git a/agent/consul/state/catalog.go b/agent/consul/state/catalog.go
index eb9673ca60..8a0f8469aa 100644
--- a/agent/consul/state/catalog.go
+++ b/agent/consul/state/catalog.go
@@ -1,6 +1,7 @@
 package state
 
 import (
+	"errors"
 	"fmt"
 	"reflect"
 	"strings"
@@ -736,34 +737,31 @@ func (s *Store) EnsureService(idx uint64, node string, svc *structs.NodeService)
 	return nil
 }
 
+var errCASCompareFailed = errors.New("compare-and-set: comparison failed")
+
 // ensureServiceCASTxn updates a service only if the existing index matches the given index.
-// Returns a bool indicating if a write happened and any error.
-func (s *Store) ensureServiceCASTxn(tx *memdb.Txn, idx uint64, node string, svc *structs.NodeService) (bool, error) {
+// Returns an error if the write didn't happen and nil if write was successful.
+func (s *Store) ensureServiceCASTxn(tx *memdb.Txn, idx uint64, node string, svc *structs.NodeService) error {
 	// Retrieve the existing service.
 	_, existing, err := firstWatchCompoundWithTxn(tx, "services", "id", &svc.EnterpriseMeta, node, svc.ID)
 	if err != nil {
-		return false, fmt.Errorf("failed service lookup: %s", err)
+		return fmt.Errorf("failed service lookup: %s", err)
 	}
 
 	// Check if the we should do the set. A ModifyIndex of 0 means that
 	// we are doing a set-if-not-exists.
 	if svc.ModifyIndex == 0 && existing != nil {
-		return false, nil
+		return errCASCompareFailed
 	}
 	if svc.ModifyIndex != 0 && existing == nil {
-		return false, nil
+		return errCASCompareFailed
 	}
 	e, ok := existing.(*structs.ServiceNode)
 	if ok && svc.ModifyIndex != 0 && svc.ModifyIndex != e.ModifyIndex {
-		return false, nil
+		return errCASCompareFailed
 	}
 
-	// Perform the update.
-	if err := s.ensureServiceTxn(tx, idx, node, svc); err != nil {
-		return false, err
-	}
-
-	return true, nil
+	return s.ensureServiceTxn(tx, idx, node, svc)
 }
 
 // ensureServiceTxn is used to upsert a service registration within an
diff --git a/agent/consul/state/catalog_test.go b/agent/consul/state/catalog_test.go
index 2627eab614..b92ada564d 100644
--- a/agent/consul/state/catalog_test.go
+++ b/agent/consul/state/catalog_test.go
@@ -2,6 +2,11 @@ package state
 
 import (
 	"fmt"
+	"reflect"
+	"sort"
+	"strings"
+	"testing"
+
 	"github.com/hashicorp/consul/agent/structs"
 	"github.com/hashicorp/consul/api"
 	"github.com/hashicorp/consul/lib"
@@ -11,10 +16,6 @@ import (
 	"github.com/pascaldekloe/goe/verify"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
-	"reflect"
-	"sort"
-	"strings"
-	"testing"
 )
 
 func makeRandomNodeID(t *testing.T) types.NodeID {
@@ -4395,9 +4396,8 @@ func TestStateStore_ensureServiceCASTxn(t *testing.T) {
 
 	// attempt to update with a 0 index
 	tx := s.db.Txn(true)
-	update, err := s.ensureServiceCASTxn(tx, 3, "node1", &ns)
-	require.False(t, update)
-	require.NoError(t, err)
+	err := s.ensureServiceCASTxn(tx, 3, "node1", &ns)
+	require.Equal(t, err, errCASCompareFailed)
 	tx.Commit()
 
 	// ensure no update happened
@@ -4411,9 +4411,8 @@ func TestStateStore_ensureServiceCASTxn(t *testing.T) {
 	ns.ModifyIndex = 99
 	// attempt to update with a non-matching index
 	tx = s.db.Txn(true)
-	update, err = s.ensureServiceCASTxn(tx, 4, "node1", &ns)
-	require.False(t, update)
-	require.NoError(t, err)
+	err = s.ensureServiceCASTxn(tx, 4, "node1", &ns)
+	require.Equal(t, err, errCASCompareFailed)
 	tx.Commit()
 
 	// ensure no update happened
@@ -4427,8 +4426,7 @@ func TestStateStore_ensureServiceCASTxn(t *testing.T) {
 	ns.ModifyIndex = 2
 	// update with the matching modify index
 	tx = s.db.Txn(true)
-	update, err = s.ensureServiceCASTxn(tx, 7, "node1", &ns)
-	require.True(t, update)
+	err = s.ensureServiceCASTxn(tx, 7, "node1", &ns)
 	require.NoError(t, err)
 	tx.Commit()
 
diff --git a/agent/consul/state/txn.go b/agent/consul/state/txn.go
index 06f20681e9..f8c02e25a9 100644
--- a/agent/consul/state/txn.go
+++ b/agent/consul/state/txn.go
@@ -230,11 +230,13 @@ func (s *Store) txnService(tx *memdb.Txn, idx uint64, op *structs.TxnServiceOp)
 		return newTxnResultFromNodeServiceEntry(entry), err
 
 	case api.ServiceCAS:
-		ok, err := s.ensureServiceCASTxn(tx, idx, op.Node, &op.Service)
-		// TODO: err != nil case is ignored
-		if !ok && err == nil {
+		err := s.ensureServiceCASTxn(tx, idx, op.Node, &op.Service)
+		switch {
+		case err == errCASCompareFailed:
 			err := fmt.Errorf("failed to set service %q on node %q, index is stale", op.Service.ID, op.Node)
 			return nil, err
+		case err != nil:
+			return nil, err
 		}
 
 		entry, err := s.getNodeServiceTxn(tx, op.Node, op.Service.ID, &op.Service.EnterpriseMeta)