diff --git a/integrations/api_oauth2_apps_test.go b/integrations/api_oauth2_apps_test.go
index 998043a6fb06..0ba56b6c9fca 100644
--- a/integrations/api_oauth2_apps_test.go
+++ b/integrations/api_oauth2_apps_test.go
@@ -92,6 +92,10 @@ func testAPIDeleteOAuth2Application(t *testing.T) {
 	session.MakeRequest(t, req, http.StatusNoContent)
 
 	models.AssertNotExistsBean(t, &models.OAuth2Application{UID: oldApp.UID, Name: oldApp.Name})
+
+	// Delete again will return not found
+	req = NewRequest(t, "DELETE", urlStr)
+	session.MakeRequest(t, req, http.StatusNotFound)
 }
 
 func testAPIGetOAuth2Application(t *testing.T) {
diff --git a/models/migrate.go b/models/migrate.go
index 9e44f32e5461..28b670747373 100644
--- a/models/migrate.go
+++ b/models/migrate.go
@@ -39,6 +39,7 @@ func InsertMilestones(ms ...*Milestone) (err error) {
 // InsertIssues insert issues to database
 func InsertIssues(issues ...*Issue) error {
 	sess := x.NewSession()
+	defer sess.Close()
 	if err := sess.Begin(); err != nil {
 		return err
 	}
@@ -194,6 +195,7 @@ func InsertPullRequests(prs ...*PullRequest) error {
 // InsertReleases migrates release
 func InsertReleases(rels ...*Release) error {
 	sess := x.NewSession()
+	defer sess.Close()
 	if err := sess.Begin(); err != nil {
 		return err
 	}
diff --git a/models/oauth2_application.go b/models/oauth2_application.go
index 1b544e4e9e19..679fdb18f957 100644
--- a/models/oauth2_application.go
+++ b/models/oauth2_application.go
@@ -235,7 +235,7 @@ func deleteOAuth2Application(sess *xorm.Session, id, userid int64) error {
 	if deleted, err := sess.Delete(&OAuth2Application{ID: id, UID: userid}); err != nil {
 		return err
 	} else if deleted == 0 {
-		return fmt.Errorf("cannot find oauth2 application")
+		return ErrOAuthApplicationNotFound{ID: id}
 	}
 	codes := make([]*OAuth2AuthorizationCode, 0)
 	// delete correlating auth codes
@@ -261,6 +261,7 @@ func deleteOAuth2Application(sess *xorm.Session, id, userid int64) error {
 // DeleteOAuth2Application deletes the application with the given id and the grants and auth codes related to it. It checks if the userid was the creator of the app.
 func DeleteOAuth2Application(id, userid int64) error {
 	sess := x.NewSession()
+	defer sess.Close()
 	if err := sess.Begin(); err != nil {
 		return err
 	}
diff --git a/routers/api/v1/user/app.go b/routers/api/v1/user/app.go
index 33b27d60e0c1..b88ed6fbd272 100644
--- a/routers/api/v1/user/app.go
+++ b/routers/api/v1/user/app.go
@@ -274,7 +274,11 @@ func DeleteOauth2Application(ctx *context.APIContext) {
 	//     "$ref": "#/responses/empty"
 	appID := ctx.ParamsInt64(":id")
 	if err := models.DeleteOAuth2Application(appID, ctx.User.ID); err != nil {
-		ctx.Error(http.StatusInternalServerError, "DeleteOauth2ApplicationByID", err)
+		if models.IsErrOAuthApplicationNotFound(err) {
+			ctx.NotFound()
+		} else {
+			ctx.Error(http.StatusInternalServerError, "DeleteOauth2ApplicationByID", err)
+		}
 		return
 	}