diff --git a/apps/provisioning_api/lib/users.php b/apps/provisioning_api/lib/users.php
index 33139bb2cef0ff6f5314238ec3d0b6aa3d6acc6a..6169ea16f9cf257a0b9ec351dad7e7884ee484d2 100644
--- a/apps/provisioning_api/lib/users.php
+++ b/apps/provisioning_api/lib/users.php
@@ -292,6 +292,10 @@ class Users {
 		if(strtolower($group) == 'admin') {
 			return new OC_OCS_Result(null, 103, 'Cannot create subadmins for admin group');
 		}
+		// We cannot be subadmin twice
+		if (OC_Subadmin::isSubAdminOfGroup($user, $group)) {
+			return new OC_OCS_Result(null, 100);
+		}
 		// Go
 		if(OC_Subadmin::createSubAdmin($user, $group)) {
 			return new OC_OCS_Result(null, 100);
diff --git a/apps/provisioning_api/tests/userstest.php b/apps/provisioning_api/tests/userstest.php
index 1abf994d92f50fee16c09b70669852bfd8301fc4..f06f853ee1fce63f967be1e47a6feffe97772c5a 100644
--- a/apps/provisioning_api/tests/userstest.php
+++ b/apps/provisioning_api/tests/userstest.php
@@ -766,4 +766,29 @@ class UsersTest extends TestCase {
 		$this->assertFalse($result->succeeded());
 		$this->assertEquals(101, $result->getStatusCode());
 	}
+
+	public function testSubAdminOfGroupAlreadySubAdmin() {
+		$user1 = $this->generateUsers();
+		$user2 = $this->generateUsers();
+		\OC_User::setUserId($user1);
+		\OC_Group::addToGroup($user1, 'admin');
+		$group1 = $this->getUniqueID();
+		\OC_Group::createGroup($group1);
+
+		//Make user2 subadmin of group1
+		$_POST['groupid'] = $group1;
+		$result = \OCA\provisioning_api\Users::addSubAdmin([
+			'userid' => $user2,
+		]);
+		$this->assertInstanceOf('OC_OCS_Result', $result);
+		$this->assertTrue($result->succeeded());
+
+		//Make user2 subadmin of group1 again
+		$_POST['groupid'] = $group1;
+		$result = \OCA\provisioning_api\Users::addSubAdmin([
+			'userid' => $user2,
+		]);
+		$this->assertInstanceOf('OC_OCS_Result', $result);
+		$this->assertTrue($result->succeeded());
+	}
 }