diff --git a/experiments/mozilla.d.ts b/experiments/mozilla.d.ts
index 4d67237d..62afba17 100644
--- a/experiments/mozilla.d.ts
+++ b/experiments/mozilla.d.ts
@@ -133,6 +133,7 @@ declare module ExtensionParentM {
     ////////////////////////////////////////////////////////////////////////////
 
     declare module apiManager {
+        // Internals that should be avoided.
         declare module global {
             const tabTracker: TabTrackerBase;
 
diff --git a/modules/dkim/verifier.mjs.js b/modules/dkim/verifier.mjs.js
index 2982f201..935ff40c 100644
--- a/modules/dkim/verifier.mjs.js
+++ b/modules/dkim/verifier.mjs.js
@@ -1036,8 +1036,7 @@ class DkimSignature {
 		let headerCanonAlgo;
 		switch (this._header.c_header) {
 			case "simple":
-				// @ts-expect-error
-				headerCanonAlgo = function (headerField) { return headerField; };
+				headerCanonAlgo = function (/** @type {string} */ headerField) { return headerField; };
 				break;
 			case "relaxed":
 				headerCanonAlgo = DkimSignature.#canonicalizationHeaderFieldRelaxed;