diff --git a/Changelog.md b/Changelog.md
index adccfc356..b08a32e69 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,12 +1,17 @@
+# v0.12.6 unreleased
+
+* [#1458](https://github.com/mbj/mutant/pull/1458)
+  Fix zombified mutant on memoized methods (only relevant for mutant developers).
+
 # v0.12.4 2024-06-30
 
-* [#1455](https://github.com/mbj/mutant/pull/1454)
+* [#1455](https://github.com/mbj/mutant/pull/1455)
 
   Fix parsing of empty rspec descriptions
 
 # v0.12.3 2024-06-10
 
-* [#1452](https://github.com/mbj/mutant/pull/1451)
+* [#1450](https://github.com/mbj/mutant/pull/1451)
 
   Remove support for EOL Ruby-3.0.
   Remove another invalid mutation to super().
diff --git a/lib/mutant/matcher/method/instance.rb b/lib/mutant/matcher/method/instance.rb
index 7df4b71de..00119d8ce 100644
--- a/lib/mutant/matcher/method/instance.rb
+++ b/lib/mutant/matcher/method/instance.rb
@@ -30,8 +30,13 @@ def self.new(scope:, target_method:)
         end
         # rubocop:enable Metrics/MethodLength
 
+        TARGET_MEMOIZER = ::Mutant::Adamantium
+
+        private_constant(*constants(false))
+
+        # mutant:disable - very hard for zombie
         def self.memoized_method?(scope, method_name)
-          scope.raw < Adamantium && scope.raw.memoized?(method_name)
+          scope.raw < TARGET_MEMOIZER && scope.raw.memoized?(method_name)
         end
         private_class_method :memoized_method?