diff --git a/src/Core/CustomMethods.php b/src/Core/CustomMethods.php
index 97f84f07d64..619f551cba0 100644
--- a/src/Core/CustomMethods.php
+++ b/src/Core/CustomMethods.php
@@ -171,11 +171,14 @@ protected function getExtraMethodConfig($method)
         }
         // Lazy define methods
         $lowerClass = strtolower(static::class);
-        if (!isset(self::class::$extra_methods[$lowerClass])) {
+        $lowerMethod = strtolower($method);
+        if (!array_key_exists($lowerClass, self::class::$extra_methods)
+            || !array_key_exists($lowerMethod, self::class::$extra_methods[$lowerClass])
+        ) {
             $this->defineMethods();
         }
 
-        return self::class::$extra_methods[$lowerClass][strtolower($method)] ?? null;
+        return self::class::$extra_methods[$lowerClass][$lowerMethod] ?? null;
     }
 
     /**
diff --git a/tests/php/Dev/DeprecationTest.php b/tests/php/Dev/DeprecationTest.php
index 03f0154fd48..a6c1e10162a 100644
--- a/tests/php/Dev/DeprecationTest.php
+++ b/tests/php/Dev/DeprecationTest.php
@@ -111,7 +111,7 @@ public function testNoticeNoReplacement()
             'Will be removed without equivalent functionality to replace it.',
             'Called from SilverStripe\Dev\Tests\DeprecationTest->testNoticeNoReplacement.'
         ]);
-        $this->expectDeprecation();
+        $this->expectException(DeprecationTestException::class);
         $this->expectDeprecationMessage($message);
         $this->enableDeprecationNotices(true);
         $ret = $this->myDeprecatedMethodNoReplacement();