diff --git a/tests/controller/CMSMainTest.php b/tests/controller/CMSMainTest.php
index fb356db1..bc145ba8 100644
--- a/tests/controller/CMSMainTest.php
+++ b/tests/controller/CMSMainTest.php
@@ -125,7 +125,7 @@ class CMSMainTest extends FunctionalTest
     {
         $page1 = $this->objFromFixture(Page::class, "page1");
         $page2 = $this->objFromFixture(Page::class, "page2");
-        $this->session()->inst_set('loggedInAs', $this->idFromFixture('SilverStripe\\Security\\Member', 'admin'));
+        $this->session()->set('loggedInAs', $this->idFromFixture('SilverStripe\\Security\\Member', 'admin'));
 
         $response = $this->get('admin/pages/publishall?confirm=1');
         $this->assertContains(
diff --git a/tests/model/SiteTreePermissionsTest.php b/tests/model/SiteTreePermissionsTest.php
index d56f5ad7..3392f780 100644
--- a/tests/model/SiteTreePermissionsTest.php
+++ b/tests/model/SiteTreePermissionsTest.php
@@ -198,7 +198,7 @@ class SiteTreePermissionsTest extends FunctionalTest
             'Users without SITETREE_GRANT_ACCESS permission cannot change "edit" permissions in cms fields'
         );
 
-        $this->session()->inst_set('loggedInAs', null);
+        $this->session()->set('loggedInAs', null);
     }
 
     public function testRestrictedViewLoggedInUsers()
diff --git a/tests/search/CMSMainSearchFormTest.php b/tests/search/CMSMainSearchFormTest.php
index 9ea76412..bbe4f81d 100644
--- a/tests/search/CMSMainSearchFormTest.php
+++ b/tests/search/CMSMainSearchFormTest.php
@@ -9,7 +9,7 @@ class CMSMainSearchFormTest extends FunctionalTest
 
     public function testTitleFilter()
     {
-        $this->session()->inst_set('loggedInAs', $this->idFromFixture('SilverStripe\\Security\\Member', 'admin'));
+        $this->session()->set('loggedInAs', $this->idFromFixture('SilverStripe\\Security\\Member', 'admin'));
 
         $response = $this->get(
             'admin/pages/SearchForm/?' .