diff --git a/packages/epub-codec/stryker.config.ts b/packages/epub-codec/stryker.config.ts
index f729f0d2c4..b9252e7e0a 100644
--- a/packages/epub-codec/stryker.config.ts
+++ b/packages/epub-codec/stryker.config.ts
@@ -2,6 +2,6 @@ import { packageStrykerConfig } from "../../stryker.shared.ts";
 
 export default packageStrykerConfig({
   vitestConfigFile: "vitest.mutation.config.ts",
-  // First CI-measured baseline: 66.23% of 2150 valid mutants, timeout share 1.3% -- break = floor(score) minus the timeout share rounded up to whole points (minimum one), per the derivation rule on PackageStrykerOptions.breakThreshold.
-  breakThreshold: 64,
+  // Every mutant is genuinely killed by a real test, or the code it would have mutated has been restructured so the mutation opportunity no longer exists as an AST node -- no per-mutant ignore comments anywhere in this package. So the gate is the literal maximum rather than a derived-with-slack figure.
+  breakThreshold: 100,
 });