diff --git a/cmd/hook.go b/cmd/hook.go
index 966e4a57c..70001f640 100644
--- a/cmd/hook.go
+++ b/cmd/hook.go
@@ -293,9 +293,32 @@ Forgejo or set your environment appropriately.`, "")
 	return nil
 }
 
+// runHookUpdate process the update hook: https://git-scm.com/docs/githooks#update
 func runHookUpdate(c *cli.Context) error {
-	// Update is empty and is kept only for backwards compatibility
-	return nil
+	// Now if we're an internal don't do anything else
+	if isInternal, _ := strconv.ParseBool(os.Getenv(repo_module.EnvIsInternal)); isInternal {
+		return nil
+	}
+
+	ctx, cancel := installSignals()
+	defer cancel()
+
+	// The last three arguments given to the hook are in order: reference name, old commit ID and new commit ID.
+	args := os.Args[len(os.Args)-3:]
+	refFullName := git.RefName(args[0])
+	newCommitID := args[2]
+
+	// Only process pull references.
+	if !refFullName.IsPull() {
+		return nil
+	}
+
+	// Deletion of the ref means that the new commit ID is only composed of '0'.
+	if strings.ContainsFunc(newCommitID, func(e rune) bool { return e != '0' }) {
+		return nil
+	}
+
+	return fail(ctx, fmt.Sprintf("The deletion of %s is skipped as it's an internal reference.", refFullName), "")
 }
 
 func runHookPostReceive(c *cli.Context) error {
diff --git a/tests/integration/git_test.go b/tests/integration/git_test.go
index e0a824671..782390002 100644
--- a/tests/integration/git_test.go
+++ b/tests/integration/git_test.go
@@ -84,6 +84,7 @@ func testGit(t *testing.T, u *url.URL) {
 		mediaTest(t, &httpContext, little, big, littleLFS, bigLFS)
 
 		t.Run("CreateAgitFlowPull", doCreateAgitFlowPull(dstPath, &httpContext, "master", "test/head"))
+		t.Run("InternalReferences", doInternalReferences(&httpContext, dstPath))
 		t.Run("BranchProtectMerge", doBranchProtectPRMerge(&httpContext, dstPath))
 		t.Run("AutoMerge", doAutoPRMerge(&httpContext, dstPath))
 		t.Run("CreatePRAndSetManuallyMerged", doCreatePRAndSetManuallyMerged(httpContext, httpContext, dstPath, "master", "test-manually-merge"))
@@ -125,6 +126,7 @@ func testGit(t *testing.T, u *url.URL) {
 			mediaTest(t, &sshContext, little, big, littleLFS, bigLFS)
 
 			t.Run("CreateAgitFlowPull", doCreateAgitFlowPull(dstPath, &sshContext, "master", "test/head2"))
+			t.Run("InternalReferences", doInternalReferences(&sshContext, dstPath))
 			t.Run("BranchProtectMerge", doBranchProtectPRMerge(&sshContext, dstPath))
 			t.Run("MergeFork", func(t *testing.T) {
 				defer tests.PrintCurrentTest(t)()
@@ -734,6 +736,20 @@ func doAutoPRMerge(baseCtx *APITestContext, dstPath string) func(t *testing.T) {
 	}
 }
 
+func doInternalReferences(ctx *APITestContext, dstPath string) func(t *testing.T) {
+	return func(t *testing.T) {
+		defer tests.PrintCurrentTest(t)()
+
+		repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{OwnerName: ctx.Username, Name: ctx.Reponame})
+		pr1 := unittest.AssertExistsAndLoadBean(t, &issues_model.PullRequest{HeadRepoID: repo.ID})
+
+		_, stdErr, gitErr := git.NewCommand(git.DefaultContext, "push", "origin").AddDynamicArguments(fmt.Sprintf(":refs/pull/%d/head", pr1.Index)).RunStdString(&git.RunOpts{Dir: dstPath})
+		assert.Error(t, gitErr)
+		assert.Contains(t, stdErr, fmt.Sprintf("remote: Forgejo: The deletion of refs/pull/%d/head is skipped as it's an internal reference.", pr1.Index))
+		assert.Contains(t, stdErr, fmt.Sprintf("[remote rejected] refs/pull/%d/head (hook declined)", pr1.Index))
+	}
+}
+
 func doCreateAgitFlowPull(dstPath string, ctx *APITestContext, baseBranch, headBranch string) func(t *testing.T) {
 	return func(t *testing.T) {
 		defer tests.PrintCurrentTest(t)()