diff --git a/tests/php/Security/VersionedMemberAuthenticatorTest.php b/tests/php/Security/VersionedMemberAuthenticatorTest.php
index a26931567..59f859f92 100644
--- a/tests/php/Security/VersionedMemberAuthenticatorTest.php
+++ b/tests/php/Security/VersionedMemberAuthenticatorTest.php
@@ -42,6 +42,14 @@ class VersionedMemberAuthenticatorTest extends SapphireTest
             return;
         }
 
+        // 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);
+
         // Enforce dummy validation (this can otherwise be influenced by recipe config)
         PasswordValidator::singleton()
             ->setMinLength(0)