diff --git a/services/repository/branch.go b/services/repository/branch.go
index fe411ae2bc2b0..280efb8ee3983 100644
--- a/services/repository/branch.go
+++ b/services/repository/branch.go
@@ -672,12 +672,20 @@ func GetBranchDivergingInfo(ctx reqctx.RequestContext, baseRepo, headRepo *repo_
 	// so at the moment, we first check the update time, then check whether the fork branch has base's head
 	diff, err := git.GetDivergingCommits(ctx, baseRepo.RepoPath(), baseGitBranch.CommitID, headGitBranch.CommitID)
 	if err != nil {
+		info.BaseIsNewer = baseGitBranch.UpdatedUnix > headGitBranch.UpdatedUnix
+		if headRepo.IsFork && info.BaseIsNewer {
+			return info, nil
+		}
 		// if the base's update time is before the fork, check whether the base's head is in the fork
+		baseGitRepo, err := gitrepo.RepositoryFromRequestContextOrOpen(ctx, baseRepo)
+		if err != nil {
+			return nil, err
+		}
 		headGitRepo, err := gitrepo.RepositoryFromRequestContextOrOpen(ctx, headRepo)
 		if err != nil {
 			return nil, err
 		}
-		baseCommitID, err := headGitRepo.ConvertToGitID(baseGitBranch.CommitID)
+		baseCommitID, err := baseGitRepo.ConvertToGitID(baseGitBranch.CommitID)
 		if err != nil {
 			return nil, err
 		}
@@ -685,12 +693,8 @@ func GetBranchDivergingInfo(ctx reqctx.RequestContext, baseRepo, headRepo *repo_
 		if err != nil {
 			return nil, err
 		}
-		hasPreviousCommit, err := headCommit.HasPreviousCommit(baseCommitID)
+		hasPreviousCommit, _ := headCommit.HasPreviousCommit(baseCommitID)
 		info.BaseIsNewer = !hasPreviousCommit
-		// make update time as last resort for divergence comparison
-		if err != nil {
-			info.BaseIsNewer = baseGitBranch.UpdatedUnix > headGitBranch.UpdatedUnix
-		}
 		return info, nil
 	}
 
diff --git a/tests/integration/repo_merge_upstream_test.go b/tests/integration/repo_merge_upstream_test.go
index 19992dc19d358..e3e423c51d5d2 100644
--- a/tests/integration/repo_merge_upstream_test.go
+++ b/tests/integration/repo_merge_upstream_test.go
@@ -4,7 +4,6 @@
 package integration
 
 import (
-	"encoding/base64"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -13,6 +12,8 @@ import (
 	"time"
 
 	auth_model "code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/models/db"
+	git_model "code.gitea.io/gitea/models/git"
 	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
@@ -36,7 +37,6 @@ func TestRepoMergeUpstream(t *testing.T) {
 			require.Equal(t, exp, resp.Body.String())
 		}
 
-		baseSession := loginUser(t, baseUser.Name)
 		session := loginUser(t, forkUser.Name)
 		token := getTokenForLoggedInUser(t, session, auth_model.AccessTokenScopeWriteRepository)
 
@@ -60,7 +60,7 @@ func TestRepoMergeUpstream(t *testing.T) {
 
 		t.Run("HeadBeforeBase", func(t *testing.T) {
 			// add a file in base repo
-			testAPINewFile(t, baseSession, baseRepo.OwnerName, baseRepo.Name, "master", "new-file.txt", "test-content-1")
+			require.NoError(t, createOrReplaceFileInBranch(baseUser, baseRepo, "new-file.txt", "master", "test-content-1"))
 
 			// the repo shows a prompt to "sync fork"
 			var mergeUpstreamLink string
@@ -83,21 +83,14 @@ func TestRepoMergeUpstream(t *testing.T) {
 
 		t.Run("BaseChangeAfterHeadChange", func(t *testing.T) {
 			// update the files: base first, head later, and check the prompt
-			testAPINewFile(t, session, forkRepo.OwnerName, forkRepo.Name, "fork-branch", "new-file-other.txt", "test-content-other")
-			baseUserToken := getTokenForLoggedInUser(t, baseSession, auth_model.AccessTokenScopeWriteRepository)
-			req := NewRequestWithJSON(t, "PUT", fmt.Sprintf("/api/v1/repos/%s/%s/contents/%s", baseRepo.OwnerName, baseRepo.Name, "new-file.txt"), &api.UpdateFileOptions{
-				DeleteFileOptions: api.DeleteFileOptions{
-					FileOptions: api.FileOptions{
-						BranchName:    "master",
-						NewBranchName: "master",
-						Message:       "Update new-file.txt",
-					},
-					SHA: "a4007b6679563f949751ed31bb371fdfb3194446",
-				},
-				ContentBase64: base64.StdEncoding.EncodeToString([]byte("test-content-2")),
-			}).
-				AddTokenAuth(baseUserToken)
-			MakeRequest(t, req, http.StatusOK)
+			require.NoError(t, createOrReplaceFileInBranch(baseUser, baseRepo, "new-file.txt", "master", "test-content-2"))
+			require.NoError(t, createOrReplaceFileInBranch(forkUser, forkRepo, "new-file-other.txt", "fork-branch", "test-content-other"))
+
+			// make sure the base branch's update time is before the fork, to make it test the complete logic
+			baseBranch := unittest.AssertExistsAndLoadBean(t, &git_model.Branch{RepoID: baseRepo.ID, Name: "master"})
+			forkBranch := unittest.AssertExistsAndLoadBean(t, &git_model.Branch{RepoID: forkRepo.ID, Name: "fork-branch"})
+			_, err := db.GetEngine(db.DefaultContext).ID(forkBranch.ID).Update(&git_model.Branch{UpdatedUnix: baseBranch.UpdatedUnix + 1})
+			require.NoError(t, err)
 
 			// the repo shows a prompt to "sync fork"
 			require.Eventually(t, func() bool {