diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6b0c9b5244..bf8d42c37b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ _Note: Gaps between patch versions are faulty/broken releases._
  * **Breaking Change**
   * `allowImportExportEverywhere` acorn option has been disabled for spec compliancy so imports and exports can **only** be present at the top level.
   * Caching is now always enabled for the require hook. It also now no longer caches require resolutions.
+  * `ignoreRegex` fallback has now been dropped from the require hook. `register(/foo/);`, `register({ ignoreRegex: /foo/ })` -> `register({ ignore: /foo/ })`.
   * Optional fast transformer backwards compatibility support has been removed. Use [loose mode](https://6to5.org/docs/usage/loose).
 
 ## 2.12.0
diff --git a/lib/6to5/register.js b/lib/6to5/register.js
index 06515c8827..c5d51c833a 100644
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -132,8 +132,6 @@ hookExtensions([".es6", ".es", ".js"]);
 module.exports = function (opts) {
   // normalise options
   opts = opts || {};
-  if (_.isRegExp(opts)) opts = { ignore: opts };
-  if (opts.ignoreRegex != null) opts.ignore = opts.ignoreRegex;
 
   if (opts.only != null) onlyRegex = util.regexify(opts.only);
   if (opts.ignore != null) ignoreRegex = util.regexify(opts.ignore);