diff --git a/src/Redmine/Api/Issue.php b/src/Redmine/Api/Issue.php
index e3dfe3a5..fde13968 100644
--- a/src/Redmine/Api/Issue.php
+++ b/src/Redmine/Api/Issue.php
@@ -393,14 +393,22 @@ private function cleanParams(array $params = [])
         if (isset($params['assigned_to'])) {
             $userApi = $this->getUserApi();
 
-            $params['assigned_to_id'] = $userApi->getIdByUsername($params['assigned_to']);
+            $params['assigned_to_id'] = array_search(
+                $params['assigned_to'],
+                $userApi->listLogins(),
+                true,
+            );
             unset($params['assigned_to']);
         }
 
         if (isset($params['author'])) {
             $userApi = $this->getUserApi();
 
-            $params['author_id'] = $userApi->getIdByUsername($params['author']);
+            $params['author_id'] = array_search(
+                $params['author'],
+                $userApi->listLogins(),
+                true,
+            );
             unset($params['author']);
         }
 
diff --git a/tests/Unit/Api/Issue/CreateTest.php b/tests/Unit/Api/Issue/CreateTest.php
index 04275625..4510d2d3 100644
--- a/tests/Unit/Api/Issue/CreateTest.php
+++ b/tests/Unit/Api/Issue/CreateTest.php
@@ -410,12 +410,12 @@ public function testCreateWithHttpClientRetrievesUserId()
             $this,
             [
                 'GET',
-                '/users.json',
+                '/users.json?limit=100&offset=0',
                 'application/json',
                 '',
                 200,
                 'application/json',
-                '{"users":[{"login":"Author Name","id":5},{"login":"Assigned to User Name","id":6}]}',
+                '{"users":[{"login":"user_5","id":5},{"login":"user_6","id":6}]}',
             ],
             [
                 'POST',
@@ -432,7 +432,7 @@ public function testCreateWithHttpClientRetrievesUserId()
         $api = new Issue($client);
 
         // Perform the tests
-        $xmlElement = $api->create(['assigned_to' => 'Assigned to User Name', 'author' => 'Author Name']);
+        $xmlElement = $api->create(['assigned_to' => 'user_6', 'author' => 'user_5']);
 
         $this->assertInstanceOf(SimpleXMLElement::class, $xmlElement);
         $this->assertXmlStringEqualsXmlString(
@@ -486,12 +486,12 @@ public function testCreateWithClientCleansParameters()
             ],
             [
                 'GET',
-                '/users.json',
+                '/users.json?limit=100&offset=0',
                 'application/json',
                 '',
                 200,
                 'application/json',
-                '{"users":[{"login":"Author Name","id":5},{"login":"Assigned to User Name","id":6}]}',
+                '{"users":[{"login":"user_5","id":5},{"login":"user_6","id":6}]}',
             ],
             [
                 'POST',
@@ -519,8 +519,8 @@ public function testCreateWithClientCleansParameters()
             'category' => 'Category Name',
             'status' => 'Status Name',
             'tracker' => 'Tracker Name',
-            'assigned_to' => 'Assigned to User Name',
-            'author' => 'Author Name',
+            'assigned_to' => 'user_6',
+            'author' => 'user_5',
         ];
 
         // Create the object under test
diff --git a/tests/Unit/Api/Issue/UpdateTest.php b/tests/Unit/Api/Issue/UpdateTest.php
index 3897ad6b..5a2e6da3 100644
--- a/tests/Unit/Api/Issue/UpdateTest.php
+++ b/tests/Unit/Api/Issue/UpdateTest.php
@@ -155,7 +155,7 @@ public function testUpdateCleansParameters()
             ],
             [
                 'GET',
-                '/users.json',
+                '/users.json?limit=100&offset=0',
                 'application/json',
                 '',
                 200,
diff --git a/tests/Unit/Api/IssueTest.php b/tests/Unit/Api/IssueTest.php
index 49b88ac8..b00d8c21 100644
--- a/tests/Unit/Api/IssueTest.php
+++ b/tests/Unit/Api/IssueTest.php
@@ -10,6 +10,7 @@
 use Redmine\Api\IssueStatus;
 use Redmine\Api\Project;
 use Redmine\Api\Tracker;
+use Redmine\Api\User;
 use Redmine\Client\Client;
 use Redmine\Http\HttpClient;
 use Redmine\Http\Response;
@@ -152,16 +153,11 @@ public function testCreateWithClientCleansParameters()
             'category' => 'Category 5 Name',
             'status' => 'Status 6 Name',
             'tracker' => 'Tracker 2 Name',
-            'assigned_to' => 'Assigned to User Name',
-            'author' => 'Author Name',
+            'assigned_to' => 'user_3',
+            'author' => 'user_4',
         ];
 
         // Create the used mock objects
-        $getIdByUsernameApi = $this->createMock('Redmine\Api\User');
-        $getIdByUsernameApi->expects($this->exactly(2))
-            ->method('getIdByUsername')
-            ->willReturn('cleanedValue');
-
         $httpClient = AssertingHttpClient::create(
             $this,
             [
@@ -200,6 +196,15 @@ public function testCreateWithClientCleansParameters()
                 'application/json',
                 '{"trackers":[{"id":2,"name":"Tracker 2 Name"}]}',
             ],
+            [
+                'GET',
+                '/users.json?limit=100&offset=0',
+                'application/json',
+                '',
+                200,
+                'application/json',
+                '{"users":[{"id":3,"login":"user_3"},{"id":4,"login":"user_4"}]}',
+            ],
         );
 
         $client = $this->createMock(Client::class);
@@ -211,7 +216,7 @@ public function testCreateWithClientCleansParameters()
                     ['issue_category', new IssueCategory($httpClient)],
                     ['issue_status', new IssueStatus($httpClient)],
                     ['tracker', new Tracker($httpClient)],
-                    ['user', $getIdByUsernameApi],
+                    ['user', new User($httpClient)],
                 ],
             )
         ;
@@ -222,7 +227,7 @@ public function testCreateWithClientCleansParameters()
                 '/issues.xml',
                 <<< XML
                 <?xml version="1.0"?>
-                <issue><project_id>1</project_id><category_id>5</category_id><status_id>6</status_id><tracker_id>2</tracker_id><assigned_to_id>cleanedValue</assigned_to_id><author_id>cleanedValue</author_id></issue>
+                <issue><project_id>1</project_id><category_id>5</category_id><status_id>6</status_id><tracker_id>2</tracker_id><assigned_to_id>3</assigned_to_id><author_id>4</author_id></issue>
 
                 XML,
             )