diff --git a/modules/indexer/issues/bleve/bleve.go b/modules/indexer/issues/bleve/bleve.go
index 3627ec5079..fd9b92c4dd 100644
--- a/modules/indexer/issues/bleve/bleve.go
+++ b/modules/indexer/issues/bleve/bleve.go
@@ -11,7 +11,6 @@ import (
 	indexer_internal "gitea.dev/modules/indexer/internal"
 	inner_bleve "gitea.dev/modules/indexer/internal/bleve"
 	"gitea.dev/modules/indexer/issues/internal"
-	"gitea.dev/modules/optional"
 	"gitea.dev/modules/util"
 
 	"github.com/blevesearch/bleve/v2"
@@ -88,6 +87,7 @@ func generateIssueIndexMapping() (mapping.IndexMapping, error) {
 	docMapping.AddFieldMappingsAt("poster_id", numberFieldMapping)
 	docMapping.AddFieldMappingsAt("assignee_id", numberFieldMapping)
 	docMapping.AddFieldMappingsAt("assignee_ids", numberFieldMapping)
+	docMapping.AddFieldMappingsAt("no_assignee", boolFieldMapping)
 	docMapping.AddFieldMappingsAt("mention_ids", numberFieldMapping)
 	docMapping.AddFieldMappingsAt("reviewed_ids", numberFieldMapping)
 	docMapping.AddFieldMappingsAt("review_requested_ids", numberFieldMapping)
@@ -261,12 +261,10 @@ func (b *Indexer) Search(ctx context.Context, options *internal.SearchOptions) (
 
 	if options.AssigneeID != "" {
 		if options.AssigneeID == "(any)" {
-			queries = append(queries, bleve.NewDisjunctionQuery(
-				inner_bleve.NumericRangeInclusiveQuery(optional.Some[int64](1), optional.None[int64](), "assignee_ids"),
-				inner_bleve.NumericRangeInclusiveQuery(optional.Some[int64](1), optional.None[int64](), "assignee_id"),
-			))
+			queries = append(queries, inner_bleve.BoolFieldQuery(false, "no_assignee"))
+		} else if options.AssigneeID == "(none)" {
+			queries = append(queries, inner_bleve.BoolFieldQuery(true, "no_assignee"))
 		} else {
-			// "(none)" becomes 0, it means no assignee
 			assigneeIDInt64, _ := strconv.ParseInt(options.AssigneeID, 10, 64)
 			queries = append(queries, bleve.NewDisjunctionQuery(
 				inner_bleve.NumericEqualityQuery(assigneeIDInt64, "assignee_ids"),
diff --git a/modules/indexer/issues/bleve/bleve_test.go b/modules/indexer/issues/bleve/bleve_test.go
index ccd7ab7b92..8d1e323125 100644
--- a/modules/indexer/issues/bleve/bleve_test.go
+++ b/modules/indexer/issues/bleve/bleve_test.go
@@ -6,7 +6,11 @@ package bleve
 import (
 	"testing"
 
+	"gitea.dev/modules/indexer/issues/internal"
 	"gitea.dev/modules/indexer/issues/internal/tests"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestBleveIndexer(t *testing.T) {
@@ -16,3 +20,56 @@ func TestBleveIndexer(t *testing.T) {
 
 	tests.TestIndexer(t, indexer)
 }
+
+func TestBleveIndexerNoAssignee(t *testing.T) {
+	dir := t.TempDir()
+	indexer := NewIndexer(dir)
+	defer indexer.Close()
+
+	_, err := indexer.Init(t.Context())
+	require.NoError(t, err)
+
+	require.NoError(t, indexer.Index(t.Context(),
+		&internal.IndexerData{ID: 1, Title: "assigned through assignee_ids", AssigneeIDs: []int64{2}},
+		&internal.IndexerData{ID: 2, Title: "unassigned", NoAssignee: true},
+	))
+
+	testCases := []struct {
+		name        string
+		opts        *internal.SearchOptions
+		expectedIDs []int64
+	}{
+		{
+			name:        "none",
+			opts:        &internal.SearchOptions{AssigneeID: "(none)"},
+			expectedIDs: []int64{2},
+		},
+		{
+			name:        "any",
+			opts:        &internal.SearchOptions{AssigneeID: "(any)"},
+			expectedIDs: []int64{1},
+		},
+		{
+			name:        "specific",
+			opts:        &internal.SearchOptions{AssigneeID: "2"},
+			expectedIDs: []int64{1},
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			result, err := indexer.Search(t.Context(), testCase.opts)
+			require.NoError(t, err)
+			assert.Equal(t, int64(len(testCase.expectedIDs)), result.Total)
+			assert.Equal(t, testCase.expectedIDs, searchResultIDs(result))
+		})
+	}
+}
+
+func searchResultIDs(result *internal.SearchResult) []int64 {
+	ids := make([]int64, 0, len(result.Hits))
+	for _, hit := range result.Hits {
+		ids = append(ids, hit.ID)
+	}
+	return ids
+}
diff --git a/modules/indexer/issues/internal/model.go b/modules/indexer/issues/internal/model.go
index a48adb3c60..a19a4b1f3c 100644
--- a/modules/indexer/issues/internal/model.go
+++ b/modules/indexer/issues/internal/model.go
@@ -36,6 +36,7 @@ type IndexerData struct {
 	PosterID           int64              `json:"poster_id"`
 	AssigneeID         int64              `json:"assignee_id"`
 	AssigneeIDs        []int64            `json:"assignee_ids"`
+	NoAssignee         bool               `json:"no_assignee"` // True if AssigneeID and AssigneeIDs are empty
 	MentionIDs         []int64            `json:"mention_ids"`
 	ReviewedIDs        []int64            `json:"reviewed_ids"`
 	ReviewRequestedIDs []int64            `json:"review_requested_ids"`
diff --git a/modules/indexer/issues/internal/tests/tests.go b/modules/indexer/issues/internal/tests/tests.go
index 276f3fb5bb..81489a7ecd 100644
--- a/modules/indexer/issues/internal/tests/tests.go
+++ b/modules/indexer/issues/internal/tests/tests.go
@@ -395,10 +395,10 @@ var cases = []*testIndexerCase{
 		Expected: func(t *testing.T, data map[int64]*internal.IndexerData, result *internal.SearchResult) {
 			assert.Len(t, result.Hits, 5)
 			for _, v := range result.Hits {
-				assert.Equal(t, int64(0), data[v.ID].AssigneeID)
+				assert.True(t, data[v.ID].NoAssignee)
 			}
 			assert.Equal(t, countIndexerData(data, func(v *internal.IndexerData) bool {
-				return v.AssigneeID == 0
+				return v.NoAssignee
 			}), result.Total)
 		},
 	},
@@ -630,10 +630,10 @@ var cases = []*testIndexerCase{
 		Expected: func(t *testing.T, data map[int64]*internal.IndexerData, result *internal.SearchResult) {
 			assert.Len(t, result.Hits, 180)
 			for _, v := range result.Hits {
-				assert.GreaterOrEqual(t, data[v.ID].AssigneeID, int64(1))
+				assert.False(t, data[v.ID].NoAssignee)
 			}
 			assert.Equal(t, countIndexerData(data, func(v *internal.IndexerData) bool {
-				return v.AssigneeID >= 1
+				return !v.NoAssignee
 			}), result.Total)
 		},
 	},
@@ -686,6 +686,7 @@ func generateDefaultIndexerData() []*internal.IndexerData {
 			for i := range projectIDs {
 				projectIDs[i] = int64(i) + 1 // projectID should not be 0
 			}
+			assigneeID := issueIndex % 10
 
 			data = append(data, &internal.IndexerData{
 				ID:                 id,
@@ -702,7 +703,8 @@ func generateDefaultIndexerData() []*internal.IndexerData {
 				ProjectIDs:         projectIDs,
 				NoProject:          len(projectIDs) == 0,
 				PosterID:           id%10 + 1, // PosterID should not be 0
-				AssigneeID:         issueIndex % 10,
+				AssigneeID:         assigneeID,
+				NoAssignee:         assigneeID == 0,
 				MentionIDs:         mentionIDs,
 				ReviewedIDs:        reviewedIDs,
 				ReviewRequestedIDs: reviewRequestedIDs,
diff --git a/modules/indexer/issues/util.go b/modules/indexer/issues/util.go
index 0db424a350..b0ed7facc7 100644
--- a/modules/indexer/issues/util.go
+++ b/modules/indexer/issues/util.go
@@ -119,6 +119,7 @@ func getIssueIndexerData(ctx context.Context, issueID int64) (*internal.IndexerD
 		PosterID:           issue.PosterID,
 		AssigneeID:         issue.AssigneeID,
 		AssigneeIDs:        assigneeIDs,
+		NoAssignee:         issue.AssigneeID == 0 && len(assigneeIDs) == 0,
 		MentionIDs:         mentionIDs,
 		ReviewedIDs:        reviewedIDs,
 		ReviewRequestedIDs: reviewRequestedIDs,