diff --git a/lib.php b/lib.php
index 102883f..2857071 100644
--- a/lib.php
+++ b/lib.php
@@ -1256,6 +1256,11 @@ function journal_pluginfile($course, $cm, $context, $filearea, $args, $forcedown
         return false;
     }
 
+    // Graders can only see entries of users in groups they have access to.
+    if ($canmanage && $USER->id != $entry->userid && !groups_user_groups_visible($course, $entry->userid, $cm)) {
+        return false;
+    }
+
     if ($filearea !== 'entry' && $filearea !== 'feedback') {
         return false;
     }
diff --git a/report.php b/report.php
index a208e8d..e216c79 100644
--- a/report.php
+++ b/report.php
@@ -82,6 +82,13 @@
 $groupmode = groups_get_activity_groupmode($cm);
 $currentgroup = groups_get_activity_group($cm, true);
 
+// In separate groups mode, a grader who is in no group and cannot access all groups must not see any entries.
+if ($groupmode == SEPARATEGROUPS && !$currentgroup && !has_capability('moodle/site:accessallgroups', $context)) {
+    echo $OUTPUT->notification(get_string('notingroup'), \core\output\notification::NOTIFY_INFO);
+    echo $OUTPUT->footer();
+    exit;
+}
+
 // Fetch users who can ADD entries (Students, but also Teachers/Admins).
 $groups = $currentgroup ? $currentgroup : '';
 $users = get_users_by_capability($context, 'mod/journal:addentries', '', '', '', '', $groups);
diff --git a/tests/behat/separate_groups.feature b/tests/behat/separate_groups.feature
new file mode 100644
index 0000000..38fe2f3
--- /dev/null
+++ b/tests/behat/separate_groups.feature
@@ -0,0 +1,43 @@
+@mod @mod_journal
+Feature: Journal entries respect separate groups
+  In order to keep entries private between groups
+  As a teacher without access to all groups
+  I must not see entries of students whose groups I am not in
+
+  Background:
+    Given the following "courses" exist:
+      | fullname | shortname | category | groupmode |
+      | Course1 | C1 | 0 | 1 |
+    And the following "users" exist:
+      | username | firstname | lastname | email |
+      | teacher1 | Teacher | 1 | teacher1@asd.com |
+      | student1 | Student | 1 | student1@asd.com |
+    And the following "course enrolments" exist:
+      | user | course | role |
+      | teacher1 | C1 | teacher |
+      | student1 | C1 | student |
+    And the following "groups" exist:
+      | name | course | idnumber |
+      | Group 1 | C1 | G1 |
+    And the following "group members" exist:
+      | user | group |
+      | student1 | G1 |
+    And the following "activities" exist:
+      | activity | name               | intro            | course | idnumber | groupmode |
+      | journal  | Test journal name  | Journal question | C1     | journal1 | 1         |
+    And I log in as "student1"
+    And I am on "Course1" course homepage
+    And I follow "Test journal name"
+    And I press "Start or edit my journal entry"
+    And I set the following fields to these values:
+      | Entry | Student 1 first reply |
+    And I press "Save changes"
+    And I log out
+
+  Scenario: Non-editing teacher in no group cannot see entries in separate groups mode
+    When I log in as "teacher1"
+    And I am on "Course1" course homepage
+    And I follow "Test journal name"
+    And I follow "View 0 journal entries"
+    Then I should see "Sorry, but you need to be part of a group to see this page."
+    And I should not see "Student 1 first reply"
diff --git a/tests/lib_test.php b/tests/lib_test.php
index 8d2c800..fff8f22 100644
--- a/tests/lib_test.php
+++ b/tests/lib_test.php
@@ -50,4 +50,38 @@ public function test_reset(): void {
         $this->assertCount(1, $status);
         $this->assertFalse($status[0]['error']);
     }
+
+    /**
+     * A grader must not be served files of an entry of a student in another separate group.
+     *
+     * @covers ::journal_pluginfile
+     */
+    public function test_pluginfile_rejects_entry_outside_graders_groups(): void {
+        global $CFG;
+        require_once($CFG->dirroot . '/mod/journal/lib.php');
+        $this->resetAfterTest();
+
+        $generator = $this->getDataGenerator();
+        $journalgenerator = $generator->get_plugin_generator('mod_journal');
+
+        $course = $generator->create_course(['groupmode' => SEPARATEGROUPS, 'groupmodeforce' => 1]);
+        $journal = $journalgenerator->create_instance(['course' => $course->id]);
+        $groupa = $generator->create_group(['courseid' => $course->id]);
+        $groupb = $generator->create_group(['courseid' => $course->id]);
+
+        $teacher = $generator->create_and_enrol($course, 'teacher');
+        $student = $generator->create_and_enrol($course, 'student');
+        $generator->create_group_member(['groupid' => $groupa->id, 'userid' => $teacher->id]);
+        $generator->create_group_member(['groupid' => $groupb->id, 'userid' => $student->id]);
+
+        $entryid = $journalgenerator->create_entry((object)['journal' => $journal->id, 'userid' => $student->id]);
+
+        $cm = get_coursemodule_from_instance('journal', $journal->id, $course->id, false, MUST_EXIST);
+        $context = \context_module::instance($cm->id);
+
+        $this->setUser($teacher);
+        foreach (['entry', 'feedback'] as $filearea) {
+            $this->assertFalse(journal_pluginfile($course, $cm, $context, $filearea, [$entryid, 'file.txt'], false));
+        }
+    }
 }