diff --git a/file/builder.go b/file/builder.go
index c6acfac5b..7bbd52a2a 100644
--- a/file/builder.go
+++ b/file/builder.go
@@ -289,8 +289,14 @@ func (b *stateBuilder) consumers() {
 	for _, c := range b.targetContent.Consumers {
 		c := c
 		if utils.Empty(c.ID) {
-			consumer, err := b.currentState.Consumers.GetByIDOrUsername(*c.Username)
-			if errors.Is(err, state.ErrNotFound) {
+			var (
+				consumer *state.Consumer
+				err      error
+			)
+			if c.Username != nil {
+				consumer, err = b.currentState.Consumers.GetByIDOrUsername(*c.Username)
+			}
+			if errors.Is(err, state.ErrNotFound) || consumer == nil {
 				if c.CustomID != nil {
 					consumer, err = b.currentState.Consumers.GetByCustomID(*c.CustomID)
 					if err == nil {
diff --git a/file/codegen/main.go b/file/codegen/main.go
index 552b70d0b..b9d5cacf0 100644
--- a/file/codegen/main.go
+++ b/file/codegen/main.go
@@ -22,12 +22,15 @@ var (
 		},
 	}
 
-	anyOfUsernameOrID = []*jsonschema.Type{
+	// consumers
+	anyOfUsernameOrCustomID = []*jsonschema.Type{
 		{
-			Required: []string{"username"},
+			Description: "at least one of custom_id or username must be set",
+			Required:    []string{"username"},
 		},
 		{
-			Required: []string{"id"},
+			Description: "at least one of custom_id or username must be set",
+			Required:    []string{"custom_id"},
 		},
 	}
 )
@@ -52,7 +55,7 @@ func main() {
 
 	schema.Definitions["FRoute"].AnyOf = anyOfNameOrID
 
-	schema.Definitions["FConsumer"].AnyOf = anyOfUsernameOrID
+	schema.Definitions["FConsumer"].AnyOf = anyOfUsernameOrCustomID
 
 	schema.Definitions["FUpstream"].Required = []string{"name"}
 
diff --git a/file/kong_json_schema.json b/file/kong_json_schema.json
index 5e68bbe5f..76d09f68a 100644
--- a/file/kong_json_schema.json
+++ b/file/kong_json_schema.json
@@ -508,12 +508,14 @@
         {
           "required": [
             "username"
-          ]
+          ],
+          "description": "at least one of custom_id or username must be set"
         },
         {
           "required": [
-            "id"
-          ]
+            "custom_id"
+          ],
+          "description": "at least one of custom_id or username must be set"
         }
       ]
     },
diff --git a/tests/integration/sync_test.go b/tests/integration/sync_test.go
index 91632e505..5e425a7f0 100644
--- a/tests/integration/sync_test.go
+++ b/tests/integration/sync_test.go
@@ -4137,7 +4137,7 @@ func Test_Sync_CreateCertificateWithSNIs(t *testing.T) {
 // test scope:
 //   - 3.0.0+
 //   - konnect
-func Test_Sync_ConsumersWithCustomIDAndUsername(t *testing.T) {
+func Test_Sync_ConsumersWithCustomIDAndOrUsername(t *testing.T) {
 	runWhenKongOrKonnect(t, ">=3.0.0")
 	setup(t)
 
@@ -4161,6 +4161,14 @@ func Test_Sync_ConsumersWithCustomIDAndUsername(t *testing.T) {
 				Username: kong.String("foo"),
 				CustomID: kong.String("bar"),
 			},
+			{
+				ID:       kong.String("18c62c3c-12cc-429a-8e5a-57f2c3691a6b"),
+				CustomID: kong.String("custom_id_only"),
+			},
+			{
+				ID:       kong.String("8ef278c9-48c1-43e1-b665-e9bc18fab4c8"),
+				Username: kong.String("username_only"),
+			},
 		},
 	}, nil)
 }
diff --git a/tests/integration/test_utils.go b/tests/integration/test_utils.go
index fd2888cbd..28d7c16c8 100644
--- a/tests/integration/test_utils.go
+++ b/tests/integration/test_utils.go
@@ -95,8 +95,16 @@ func sortSlices(x, y interface{}) bool {
 		yName = *yEntity.Prefix
 	case *kong.Consumer:
 		yEntity := y.(*kong.Consumer)
-		xName = *xEntity.Username
-		yName = *yEntity.Username
+		if xEntity.Username != nil {
+			xName = *xEntity.Username
+		} else {
+			xName = *xEntity.ID
+		}
+		if yEntity.Username != nil {
+			yName = *yEntity.Username
+		} else {
+			yName = *yEntity.ID
+		}
 	case *kong.ConsumerGroup:
 		yEntity := y.(*kong.ConsumerGroup)
 		xName = *xEntity.Name
diff --git a/tests/integration/testdata/sync/024-consumers-with-custom_id-and-username/kong3x.yaml b/tests/integration/testdata/sync/024-consumers-with-custom_id-and-username/kong3x.yaml
index f20ee8080..c858f03d1 100644
--- a/tests/integration/testdata/sync/024-consumers-with-custom_id-and-username/kong3x.yaml
+++ b/tests/integration/testdata/sync/024-consumers-with-custom_id-and-username/kong3x.yaml
@@ -6,3 +6,7 @@ consumers:
 - custom_id: bar
   id: 7820f383-7b77-4fcc-af7f-14ff3e256693
   username: foo
+- custom_id: custom_id_only
+  id: 18c62c3c-12cc-429a-8e5a-57f2c3691a6b
+- id: 8ef278c9-48c1-43e1-b665-e9bc18fab4c8
+  username: username_only
\ No newline at end of file
diff --git a/types/consumer.go b/types/consumer.go
index 6d8202ff5..4d5b52c1c 100644
--- a/types/consumer.go
+++ b/types/consumer.go
@@ -181,12 +181,38 @@ func (d *consumerDiffer) DuplicatesDeletes() ([]crud.Event, error) {
 }
 
 func (d *consumerDiffer) deleteDuplicateConsumer(targetConsumer *state.Consumer) (*crud.Event, error) {
-	currentConsumer, err := d.currentState.Consumers.GetByIDOrUsername(*targetConsumer.Username)
-	if errors.Is(err, state.ErrNotFound) {
-		return nil, nil
+	var (
+		idOrUsername string
+
+		currentConsumer *state.Consumer
+		err             error
+	)
+
+	if targetConsumer.Username != nil {
+		idOrUsername = *targetConsumer.Username
+	} else if targetConsumer.ID != nil {
+		idOrUsername = *targetConsumer.ID
+	}
+
+	if idOrUsername != "" {
+		currentConsumer, err = d.currentState.Consumers.GetByIDOrUsername(idOrUsername)
+	}
+	if errors.Is(err, state.ErrNotFound) || idOrUsername == "" {
+		if targetConsumer.CustomID != nil {
+			currentConsumer, err = d.currentState.Consumers.GetByCustomID(*targetConsumer.CustomID)
+			if errors.Is(err, state.ErrNotFound) {
+				return nil, nil
+			}
+			if err != nil {
+				return nil, fmt.Errorf("error looking up consumer by custom_id %q: %w",
+					*targetConsumer.Username, err)
+			}
+		} else {
+			return nil, nil
+		}
 	}
 	if err != nil {
-		return nil, fmt.Errorf("error looking up consumer %q: %w",
+		return nil, fmt.Errorf("error looking up consumer by username or id %q: %w",
 			*targetConsumer.Username, err)
 	}