diff --git a/models/pull.go b/models/pull.go
index 133f196aaed4..a1fd7c3e4186 100644
--- a/models/pull.go
+++ b/models/pull.go
@@ -212,12 +212,21 @@ func (pr *PullRequest) GetDefaultMergeMessage() string {
 		log.Error("Cannot load issue %d for PR id %d: Error: %v", pr.IssueID, pr.ID, err)
 		return ""
 	}
-
-	if pr.BaseRepoID == pr.HeadRepoID {
-		return fmt.Sprintf("Merge pull request '%s' (#%d) from %s into %s", pr.Issue.Title, pr.Issue.Index, pr.HeadBranch, pr.BaseBranch)
+	if err := pr.LoadBaseRepo(); err != nil {
+		log.Error("LoadBaseRepo: %v", err)
+		return ""
 	}
 
-	return fmt.Sprintf("Merge pull request '%s' (#%d) from %s:%s into %s", pr.Issue.Title, pr.Issue.Index, pr.HeadRepo.FullName(), pr.HeadBranch, pr.BaseBranch)
+	issueReference := "#"
+	if pr.BaseRepo.UnitEnabled(UnitTypeExternalTracker) {
+		issueReference = "!"
+	}
+
+	if pr.BaseRepoID == pr.HeadRepoID {
+		return fmt.Sprintf("Merge pull request '%s' (%s%d) from %s into %s", pr.Issue.Title, issueReference, pr.Issue.Index, pr.HeadBranch, pr.BaseBranch)
+	}
+
+	return fmt.Sprintf("Merge pull request '%s' (%s%d) from %s:%s into %s", pr.Issue.Title, issueReference, pr.Issue.Index, pr.HeadRepo.FullName(), pr.HeadBranch, pr.BaseBranch)
 }
 
 // ReviewCount represents a count of Reviews
diff --git a/models/pull_test.go b/models/pull_test.go
index 3cc6abfec7e2..5eaeb60e6728 100644
--- a/models/pull_test.go
+++ b/models/pull_test.go
@@ -234,3 +234,36 @@ func TestPullRequest_GetWorkInProgressPrefixWorkInProgress(t *testing.T) {
 	pr.Issue.Title = "[wip] " + original
 	assert.Equal(t, "[wip]", pr.GetWorkInProgressPrefix())
 }
+
+func TestPullRequest_GetDefaultMergeMessage_InternalTracker(t *testing.T) {
+	assert.NoError(t, PrepareTestDatabase())
+	pr := AssertExistsAndLoadBean(t, &PullRequest{ID: 2}).(*PullRequest)
+
+	assert.Equal(t, "Merge pull request 'issue3' (#3) from branch2 into master", pr.GetDefaultMergeMessage())
+
+	pr.BaseRepoID = 1
+	pr.HeadRepoID = 2
+	assert.Equal(t, "Merge pull request 'issue3' (#3) from user2/repo1:branch2 into master", pr.GetDefaultMergeMessage())
+}
+
+func TestPullRequest_GetDefaultMergeMessage_ExternalTracker(t *testing.T) {
+	assert.NoError(t, PrepareTestDatabase())
+
+	externalTracker := RepoUnit{
+		Type: UnitTypeExternalTracker,
+		Config: &ExternalTrackerConfig{
+			ExternalTrackerFormat: "https://someurl.com/{user}/{repo}/{issue}",
+		},
+	}
+	baseRepo := &Repository{Name: "testRepo", ID: 1}
+	baseRepo.Owner = &User{Name: "testOwner"}
+	baseRepo.Units = []*RepoUnit{&externalTracker}
+
+	pr := AssertExistsAndLoadBean(t, &PullRequest{ID: 2, BaseRepo: baseRepo}).(*PullRequest)
+
+	assert.Equal(t, "Merge pull request 'issue3' (!3) from branch2 into master", pr.GetDefaultMergeMessage())
+
+	pr.BaseRepoID = 1
+	pr.HeadRepoID = 2
+	assert.Equal(t, "Merge pull request 'issue3' (!3) from user2/repo1:branch2 into master", pr.GetDefaultMergeMessage())
+}