diff --git a/mod/forum/classes/post_form.php b/mod/forum/classes/post_form.php
index 80c219a1fcd..ba064a84554 100644
--- a/mod/forum/classes/post_form.php
+++ b/mod/forum/classes/post_form.php
@@ -162,13 +162,21 @@ class mod_forum_post_form extends moodleform {
             $mform->setConstants(array('timestart'=> 0, 'timeend'=>0));
         }
 
-        if (groups_get_activity_groupmode($cm, $course)) { // hack alert
+        if ($groupmode = groups_get_activity_groupmode($cm, $course)) { // hack alert
             $groupdata = groups_get_activity_allowed_groups($cm);
             $groupcount = count($groupdata);
+            $groupinfo = array();
             $modulecontext = context_module::instance($cm->id);
-            $contextcheck = has_capability('mod/forum:movediscussions', $modulecontext) && empty($post->parent) && $groupcount;
-            if ($contextcheck) {
+
+            // Check whether the user has access to all groups in this forum from the accessallgroups cap.
+            if ($groupmode == VISIBLEGROUPS || has_capability('moodle/site:accessallgroups', $modulecontext)) {
+                // Only allow posting to all groups if the user has access to all groups.
                 $groupinfo = array('0' => get_string('allparticipants'));
+                $groupcount++;
+            }
+
+            $contextcheck = has_capability('mod/forum:movediscussions', $modulecontext) && empty($post->parent) && $groupcount > 1;
+            if ($contextcheck) {
                 foreach ($groupdata as $grouptemp) {
                     $groupinfo[$grouptemp->id] = $grouptemp->name;
                 }
diff --git a/mod/forum/tests/behat/separate_group_discussions.feature b/mod/forum/tests/behat/separate_group_discussions.feature
new file mode 100644
index 00000000000..3b5978f4441
--- /dev/null
+++ b/mod/forum/tests/behat/separate_group_discussions.feature
@@ -0,0 +1,84 @@
+@mod @mod_forum
+Feature: Posting to all groups in a separate group discussion is restricted to users with access to all groups
+  In order to post to all groups in a forum with separate groups
+  As a teacher
+  I need to have the accessallgroups capability or be a member of all of the groups
+
+  Background:
+    Given the following "users" exist:
+      | username | firstname | lastname | email |
+      | teacher1 | Teacher | 1 | teacher1@asd.com |
+      | noneditor1 | Non-editing teacher | 1 | noneditor1@asd.com |
+      | noneditor2 | Non-editing teacher | 2 | noneditor2@asd.com |
+      | student1 | Student | 1 | student1@asd.com |
+    And the following "courses" exist:
+      | fullname | shortname | category |
+      | Course 1 | C1 | 0 |
+    And the following "course enrolments" exist:
+      | user | course | role |
+      | teacher1 | C1 | editingteacher |
+      | noneditor1 | C1 | teacher |
+      | noneditor2 | C1 | teacher |
+      | student1 | C1 | student |
+    And the following "groups" exist:
+      | name | course | idnumber |
+      | Group A | C1 | G1 |
+      | Group B | C1 | G2 |
+      | Group C | C1 | G3 |
+    And the following "group members" exist:
+      | user | group |
+      | teacher1 | G1 |
+      | teacher1 | G2 |
+      | noneditor1 | G1 |
+      | noneditor1 | G2 |
+      | noneditor1 | G3 |
+      | noneditor2 | G1 |
+      | noneditor2 | G2 |
+      | student1 | G1 |
+      | student1 | G2 |
+    And I log in as "teacher1"
+    And I follow "Course 1"
+    And I turn editing mode on
+    And I add a "Forum" to section "1" and I fill the form with:
+      | Forum name | Standard forum name |
+      | Forum type | Standard forum for general use |
+      | Description | Standard forum description |
+      | Group mode | Separate groups |
+    And I log out
+
+  Scenario: Teacher with accessallgroups can post in all groups
+    Given I log in as "teacher1"
+    And I follow "Course 1"
+    And I follow "Standard forum name"
+    When I click on "Add a new discussion topic" "button"
+    Then the "Group" select box should contain "All participants"
+    And the "Group" select box should contain "Group A"
+    And the "Group" select box should contain "Group B"
+
+  @javascript
+  Scenario: Teacher in all groups but without accessallgroups can only post in their groups
+    And I log in as "admin"
+    And I set the following system permissions of "Non-editing teacher" role:
+      | moodle/site:accessallgroups | Prohibit |
+    And I log out
+    Given I log in as "noneditor1"
+    And I follow "Course 1"
+    And I follow "Standard forum name"
+    When I click on "Add a new discussion topic" "button"
+    Then the "Group" select box should not contain "All participants"
+    And the "Group" select box should contain "Group A"
+    And the "Group" select box should contain "Group B"
+
+  @javascript
+  Scenario: Teacher in some groups and without accessallgroups can only post in their groups
+    And I log in as "admin"
+    And I set the following system permissions of "Non-editing teacher" role:
+      | moodle/site:accessallgroups | Prohibit |
+    And I log out
+    Given I log in as "noneditor1"
+    And I follow "Course 1"
+    And I follow "Standard forum name"
+    When I click on "Add a new discussion topic" "button"
+    Then the "Group" select box should not contain "All participants"
+    And the "Group" select box should contain "Group A"
+    And the "Group" select box should contain "Group B"
diff --git a/mod/forum/tests/behat/separate_group_single_group_discussions.feature b/mod/forum/tests/behat/separate_group_single_group_discussions.feature
new file mode 100644
index 00000000000..d8745d11a77
--- /dev/null
+++ b/mod/forum/tests/behat/separate_group_single_group_discussions.feature
@@ -0,0 +1,84 @@
+@mod @mod_forum
+Feature: Posting to groups in a separate group discussion when restricted to groupings
+  In order to post to groups in a forum with separate groups and groupings
+  As a teacher
+  I need to have groups configured to post to a group
+
+  Background:
+    Given the following "users" exist:
+      | username | firstname | lastname | email            |
+      | teacher1 | teacher1  | teacher1 | teacher1@asd.com |
+    And the following "courses" exist:
+      | fullname | shortname | category |
+      | Course 1 | C1 | 0 |
+    And the following "course enrolments" exist:
+      | user | course | role |
+      | teacher1 | C1 | teacher |
+    And the following "groups" exist:
+      | name | course | idnumber |
+      | G1G1 | C1 | G1G1 |
+      | G1G2 | C1 | G1G2 |
+      | G2G1 | C1 | G2G1 |
+    And the following "groupings" exist:
+      | name | course | idnumber |
+      | G1   | C1     | G1       |
+      | G2   | C1     | G2       |
+    And the following "group members" exist:
+      | user        | group |
+      | teacher1    | G1G1  |
+      | teacher1    | G1G2  |
+      | teacher1    | G2G1  |
+    And the following "grouping groups" exist:
+      | grouping | group |
+      | G1       | G1G1    |
+      | G1       | G1G2    |
+      | G2       | G2G1    |
+    And I log in as "admin"
+    And I follow "Course 1"
+    And I turn editing mode on
+    And I add a "Forum" to section "1" and I fill the form with:
+      | Forum name  | Multiple groups forum             |
+      | Forum type  | Standard forum for general use    |
+      | Description | Standard forum description        |
+      | Group mode  | Separate groups                   |
+      | Grouping    | G1                                |
+    And I add a "Forum" to section "1" and I fill the form with:
+      | Forum name  | Single groups forum               |
+      | Forum type  | Standard forum for general use    |
+      | Description | Standard forum description        |
+      | Group mode  | Separate groups                   |
+      | Grouping    | G2                                |
+    And I log out
+
+  Scenario: Teacher with accessallgroups can post in all groups
+    Given I log in as "teacher1"
+    And I follow "Course 1"
+    And I follow "Multiple groups forum"
+    When I click on "Add a new discussion topic" "button"
+    Then the "Group" select box should contain "All participants"
+    And the "Group" select box should contain "G1G1"
+    And the "Group" select box should contain "G1G2"
+    And I follow "Course 1"
+    And I follow "Single groups forum"
+    And I click on "Add a new discussion topic" "button"
+    And the "Group" select box should contain "All participants"
+    And the "Group" select box should contain "G2G1"
+
+  @javascript
+  Scenario: Teacher in all groups but without accessallgroups can post in either group but not to All Participants
+    And I log in as "admin"
+    And I set the following system permissions of "Non-editing teacher" role:
+      | moodle/site:accessallgroups | Prohibit |
+    And I log out
+    Given I log in as "teacher1"
+    And I follow "Course 1"
+    And I follow "Multiple groups forum"
+    When I click on "Add a new discussion topic" "button"
+    Then the "Group" select box should not contain "All participants"
+    And the "Group" select box should contain "G1G1"
+    And the "Group" select box should contain "G1G2"
+    And I follow "Course 1"
+    And I follow "Single groups forum"
+    And I click on "Add a new discussion topic" "button"
+    And I should see "G2G1"
+    And "Group" "select" should not exist