diff --git a/tests/php/Security/VersionedMemberAuthenticatorTest.php b/tests/php/Security/VersionedMemberAuthenticatorTest.php
index 0a3dbb215..5cc38cd6f 100644
--- a/tests/php/Security/VersionedMemberAuthenticatorTest.php
+++ b/tests/php/Security/VersionedMemberAuthenticatorTest.php
@@ -32,6 +32,14 @@ class VersionedMemberAuthenticatorTest extends SapphireTest
 
         // Remove password validation
         Member::set_password_validator(null);
+
+        // Explicity add the Versioned extension to Member, even though it's already in $required_extensions.
+        // This is done to call `unset(self::class::$extra_methods[strtolower($subclass)]);` in
+        // Extensible::add_extension() so when CustomMethods::getExtraMethodConfig() updates the $extra_methods
+        // it will include methods of Versioned such as publishSingle()
+        // This issue will only occur when running subsequent unit test classes in the same process, rather than this
+        // this unit test class in isolation
+        Member::add_extension(Versioned::class);
     }
 
     protected function tearDown(): void