diff --git a/modules/indexer/issues/dboptions.go b/modules/indexer/issues/dboptions.go
index 4a98b4588a..15363847ce 100644
--- a/modules/indexer/issues/dboptions.go
+++ b/modules/indexer/issues/dboptions.go
@@ -38,6 +38,12 @@ func ToSearchOptions(keyword string, opts *issues_model.IssuesOptions) *SearchOp
 		searchOpt.MilestoneIDs = opts.MilestoneIDs
 	}
 
+	if opts.ProjectID > 0 {
+		searchOpt.ProjectID = optional.Some(opts.ProjectID)
+	} else if opts.ProjectID == -1 { // FIXME: this is inconsistent from other places
+		searchOpt.ProjectID = optional.Some[int64](0) // Those issues with no project(projectid==0)
+	}
+
 	// See the comment of issues_model.SearchOptions for the reason why we need to convert
 	convertID := func(id int64) optional.Option[int64] {
 		if id > 0 {
@@ -49,7 +55,6 @@ func ToSearchOptions(keyword string, opts *issues_model.IssuesOptions) *SearchOp
 		return nil
 	}
 
-	searchOpt.ProjectID = convertID(opts.ProjectID)
 	searchOpt.ProjectBoardID = convertID(opts.ProjectBoardID)
 	searchOpt.PosterID = convertID(opts.PosterID)
 	searchOpt.AssigneeID = convertID(opts.AssigneeID)
diff --git a/tests/integration/issue_test.go b/tests/integration/issue_test.go
index 94ba670b71..3f61dafbf0 100644
--- a/tests/integration/issue_test.go
+++ b/tests/integration/issue_test.go
@@ -17,6 +17,7 @@ import (
 
 	"code.gitea.io/gitea/models/db"
 	issues_model "code.gitea.io/gitea/models/issues"
+	project_model "code.gitea.io/gitea/models/project"
 	repo_model "code.gitea.io/gitea/models/repo"
 	unit_model "code.gitea.io/gitea/models/unit"
 	"code.gitea.io/gitea/models/unittest"
@@ -121,6 +122,57 @@ func TestViewIssuesKeyword(t *testing.T) {
 	})
 }
 
+func TestViewIssuesSearchOptions(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+
+	// there are two issues in repo1, both bound to a project. Add one
+	// that is not bound to any project.
+	_, issueNoProject := testIssueWithBean(t, "user2", 1, "Title", "Description")
+
+	t.Run("All issues", func(t *testing.T) {
+		req := NewRequestf(t, "GET", "%s/issues?state=all", repo.Link())
+		resp := MakeRequest(t, req, http.StatusOK)
+		htmlDoc := NewHTMLParser(t, resp.Body)
+		issuesSelection := getIssuesSelection(t, htmlDoc)
+		assert.EqualValues(t, 3, issuesSelection.Length())
+	})
+
+	t.Run("Issues with no project", func(t *testing.T) {
+		req := NewRequestf(t, "GET", "%s/issues?state=all&project=-1", repo.Link())
+		resp := MakeRequest(t, req, http.StatusOK)
+		htmlDoc := NewHTMLParser(t, resp.Body)
+		issuesSelection := getIssuesSelection(t, htmlDoc)
+		assert.EqualValues(t, 1, issuesSelection.Length())
+		issuesSelection.Each(func(_ int, selection *goquery.Selection) {
+			issue := getIssue(t, repo.ID, selection)
+			assert.Equal(t, issueNoProject.ID, issue.ID)
+		})
+	})
+
+	t.Run("Issues with a specific project", func(t *testing.T) {
+		project := unittest.AssertExistsAndLoadBean(t, &project_model.Project{ID: 1})
+
+		req := NewRequestf(t, "GET", "%s/issues?state=all&project=%d", repo.Link(), project.ID)
+		resp := MakeRequest(t, req, http.StatusOK)
+		htmlDoc := NewHTMLParser(t, resp.Body)
+		issuesSelection := getIssuesSelection(t, htmlDoc)
+		assert.EqualValues(t, 2, issuesSelection.Length())
+		found := map[int64]bool{
+			1: false,
+			5: false,
+		}
+		issuesSelection.Each(func(_ int, selection *goquery.Selection) {
+			issue := getIssue(t, repo.ID, selection)
+			found[issue.ID] = true
+		})
+		assert.EqualValues(t, 2, len(found))
+		assert.True(t, found[1])
+		assert.True(t, found[5])
+	})
+}
+
 func TestNoLoginViewIssue(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()