diff --git a/mod/forum/classes/local/vaults/discussion_list.php b/mod/forum/classes/local/vaults/discussion_list.php
index 9bd2aca9e65..6cfcebf2f58 100644
--- a/mod/forum/classes/local/vaults/discussion_list.php
+++ b/mod/forum/classes/local/vaults/discussion_list.php
@@ -137,9 +137,9 @@ class discussion_list extends db_table_vault {
         $issortbyreplies = in_array($sortsql, $sortkeys);
 
         $tables = $thistable->get_from_sql();
-        $tables .= ' JOIN {user} fa ON fa.id = ' . $alias . '.userid';
-        $tables .= ' JOIN {user} la ON la.id = ' . $alias . '.usermodified';
         $tables .= ' JOIN ' . $posttable->get_from_sql() . ' ON fp.id = ' . $alias . '.firstpost';
+        $tables .= ' JOIN {user} fa ON fa.id = fp.userid';
+        $tables .= ' JOIN {user} la ON la.id = ' . $alias . '.usermodified';
         $tables .= $favsql;
 
         if ($issortbyreplies) {
diff --git a/mod/forum/tests/behat/split_forum_discussion.feature b/mod/forum/tests/behat/split_forum_discussion.feature
index e664f8a56d9..51bae11ec85 100644
--- a/mod/forum/tests/behat/split_forum_discussion.feature
+++ b/mod/forum/tests/behat/split_forum_discussion.feature
@@ -9,6 +9,7 @@ Feature: Forum discussions can be split
       | username | firstname | lastname | email |
       | teacher1 | Teacher | 1 | teacher1@example.com |
       | student1 | Student | 1 | student1@example.com |
+      | student2 | Student | 2 | student2@example.com |
     And the following "courses" exist:
       | fullname | shortname | category |
       | Science 101 | C1 | 0 |
@@ -16,6 +17,7 @@ Feature: Forum discussions can be split
       | user | course | role |
       | teacher1 | C1 | editingteacher |
       | student1 | C1 | student |
+      | student2 | C1 | student |
     And I log in as "teacher1"
     And I am on "Science 101" course homepage with editing mode on
     And I add a "Forum" to section "1" and I fill the form with:
@@ -31,6 +33,16 @@ Feature: Forum discussions can be split
     And I reply "Photosynethis discussion" post from "Study discussions" forum with:
       | Message | Can anyone tell me which number is the mass number in the periodic table? |
     And I log out
+    And I log in as "student2"
+    And I am on "Science 101" course homepage
+    And I follow "Study discussions"
+    And I follow "Photosynethis discussion"
+    And I click on "Reply" "link" in the "//div[contains(concat(' ', normalize-space(@class), ' '), ' forumpost ')][contains(., 'Can anyone tell me which number is the mass number in the periodic table?')]" "xpath_element"
+    And I wait to be redirected
+    And I set the following fields to these values:
+      | Message | I would also like to know this |
+    And I press "Post to forum"
+    And I log out
 
   Scenario: Split a forum discussion
     Given I log in as "teacher1"
@@ -44,4 +56,9 @@ Feature: Forum discussions can be split
     Then I should see "Mass number in periodic table"
     And I follow "Study discussions"
     And I should see "Teacher 1" in the "Photosynethis" "table_row"
+    # Confirm that the last post author has been updated.
+    And I should not see "Student 2" in the "Photosynethis" "table_row"
+    # Confirm that the corrent author has been shown for the new split discussion.
     And I should see "Student 1" in the "Mass number in periodic table" "table_row"
+    # Confirm that the last post author has been updated for the new discussion.
+    And I should see "Student 2" in the "Mass number in periodic table" "table_row"