diff --git a/user/lib.php b/user/lib.php
index 96ab8c28ea9..6f82000dd40 100644
--- a/user/lib.php
+++ b/user/lib.php
@@ -373,23 +373,28 @@ function user_get_user_details($user, $course = null, array $userfields = array(
         return null;
     }
 
-    $userdetails = array();
-    $userdetails['id'] = $user->id;
+    // User ID and fullname are always included.
+    $userdetails = [
+        'id' => $user->id,
+        'fullname' => fullname($user, $canviewfullnames),
+    ];
+
+    // User first/lastname included if capability check passes, or the same is present in fullname.
+    $dummyusername = core_user::get_dummy_fullname($context, ['override' => $canviewfullnames]);
+    if (in_array('firstname', $userfields) &&
+            ($canviewfullnames || core_text::strrpos($dummyusername, 'firstname') !== false)) {
+        $userdetails['firstname'] = $user->firstname;
+    }
+    if (in_array('lastname', $userfields) &&
+            ($canviewfullnames || core_text::strrpos($dummyusername, 'lastname') !== false)) {
+        $userdetails['lastname'] = $user->lastname;
+    }
 
     if (in_array('username', $userfields)) {
         if ($currentuser or has_capability('moodle/user:viewalldetails', $context)) {
             $userdetails['username'] = $user->username;
         }
     }
-    if ($isadmin or $canviewfullnames) {
-        if (in_array('firstname', $userfields)) {
-            $userdetails['firstname'] = $user->firstname;
-        }
-        if (in_array('lastname', $userfields)) {
-            $userdetails['lastname'] = $user->lastname;
-        }
-    }
-    $userdetails['fullname'] = fullname($user, $canviewfullnames);
 
     if (in_array('customfields', $userfields)) {
         $categories = profile_get_user_fields_with_data_by_category($user->id);
diff --git a/user/tests/userlib_test.php b/user/tests/userlib_test.php
index 337ecf7fadb..edf1de5c185 100644
--- a/user/tests/userlib_test.php
+++ b/user/tests/userlib_test.php
@@ -850,16 +850,21 @@ final class userlib_test extends \advanced_testcase {
         accesslib_clear_all_caches_for_unit_testing();
 
         // Get student details as a user with super system capabilities.
+        $this->setAdminUser();
         $result = user_get_user_details($student, $course1);
         $this->assertEquals($student->id, $result['id']);
         $this->assertEquals($studentfullname, $result['fullname']);
+        $this->assertEquals($student->firstname, $result['firstname']);
+        $this->assertEquals($student->lastname, $result['lastname']);
         $this->assertEquals($course1->id, $result['enrolledcourses'][0]['id']);
 
-        $this->setUser($teacher);
         // Get student details as a user who can only see this user in a course.
+        $this->setUser($teacher);
         $result = user_get_user_details($student, $course1);
         $this->assertEquals($student->id, $result['id']);
         $this->assertEquals($studentfullname, $result['fullname']);
+        $this->assertEquals($student->firstname, $result['firstname']);
+        $this->assertEquals($student->lastname, $result['lastname']);
         $this->assertEquals($course1->id, $result['enrolledcourses'][0]['id']);
 
         // Get student details with required fields.
@@ -867,6 +872,23 @@ final class userlib_test extends \advanced_testcase {
         $this->assertCount(2, $result);
         $this->assertEquals($student->id, $result['id']);
         $this->assertEquals($studentfullname, $result['fullname']);
+        $this->assertArrayNotHasKey('firstname', $result);
+        $this->assertArrayNotHasKey('lastname', $result);
+        $this->assertArrayNotHasKey('enrolledcourses', $result);
+
+        // Change fullname display format for a user with viewfullnames capability.
+        set_config('fullnamedisplay', 'firstname');
+        $result = user_get_user_details($student, $course1);
+        $this->assertEquals($studentfullname, $result['fullname']);
+        $this->assertEquals($student->firstname, $result['firstname']);
+        $this->assertEquals($student->lastname, $result['lastname']);
+
+        // Now check for a user without viewfullnames capability.
+        $this->setUser($student);
+        $result = user_get_user_details($teacher, $course1);
+        $this->assertEquals($teacher->firstname, $result['fullname']);
+        $this->assertEquals($teacher->firstname, $result['firstname']);
+        $this->assertArrayNotHasKey('lastname', $result);
 
         // Get exception for invalid required fields.
         $this->expectException('moodle_exception');