diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index fba416d4db35d6..3a983fd7bcf00f 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -217,16 +217,6 @@ function tryExtensions(p, exts, isMain) {
   return false;
 }
 
-function readExtensions() {
-  const exts = Object.keys(Module._extensions);
-  for (var i = 0, j = 0; i < exts.length; ++i) {
-    if (path.extname(exts[i]) === '')
-      exts[j++] = exts[i];
-  }
-  exts.length = j;
-  return exts;
-}
-
 var warned = false;
 Module._findPath = function(request, paths, isMain) {
   if (path.isAbsolute(request)) {
@@ -283,7 +273,7 @@ Module._findPath = function(request, paths, isMain) {
       if (!filename) {
         // try it with each of the extensions
         if (exts === undefined)
-          exts = readExtensions();
+          exts = Object.keys(Module._extensions);
         filename = tryExtensions(basePath, exts, isMain);
       }
     }
@@ -291,7 +281,7 @@ Module._findPath = function(request, paths, isMain) {
     if (!filename && rc === 1) {  // Directory.
       // try it with each of the extensions at "index"
       if (exts === undefined)
-        exts = readExtensions();
+        exts = Object.keys(Module._extensions);
       filename = tryPackage(basePath, exts, isMain);
       if (!filename) {
         filename = tryExtensions(path.resolve(basePath, 'index'), exts, isMain);
diff --git a/test/known_issues/test-module-deleted-extensions.js b/test/known_issues/test-module-deleted-extensions.js
new file mode 100644
index 00000000000000..3a51e8725eec60
--- /dev/null
+++ b/test/known_issues/test-module-deleted-extensions.js
@@ -0,0 +1,18 @@
+'use strict';
+// Refs: https://github.com/nodejs/node/issues/4778
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+const path = require('path');
+const tmpdir = require('../common/tmpdir');
+const file = path.join(tmpdir.path, 'test-extensions.foo.bar');
+
+tmpdir.refresh();
+fs.writeFileSync(file, '', 'utf8');
+require.extensions['.foo.bar'] = (module, path) => {};
+delete require.extensions['.foo.bar'];
+require.extensions['.bar'] = common.mustCall((module, path) => {
+  assert.strictEqual(module.id, file);
+  assert.strictEqual(path, file);
+});
+require(path.join(tmpdir.path, 'test-extensions'));
diff --git a/test/parallel/test-module-deleted-extensions.js b/test/parallel/test-module-deleted-extensions.js
deleted file mode 100644
index f14da0a70f7656..00000000000000
--- a/test/parallel/test-module-deleted-extensions.js
+++ /dev/null
@@ -1,58 +0,0 @@
-'use strict';
-
-// Refs: https://github.com/nodejs/node/issues/4778
-
-const common = require('../common');
-const assert = require('assert');
-const fs = require('fs');
-const path = require('path');
-const tmpdir = require('../common/tmpdir');
-const file = path.join(tmpdir.path, 'test-extensions.foo.bar');
-
-tmpdir.refresh();
-fs.writeFileSync(file, '', 'utf8');
-
-{
-  require.extensions['.bar'] = common.mustNotCall();
-  require.extensions['.foo.bar'] = common.mustNotCall();
-  const modulePath = path.join(tmpdir.path, 'test-extensions');
-  assert.throws(
-    () => require(modulePath),
-    new Error(`Cannot find module '${modulePath}'`)
-  );
-}
-
-{
-  delete require.extensions['.bar'];
-  require.extensions['.foo.bar'] = common.mustNotCall();
-  const modulePath = path.join(tmpdir.path, 'test-extensions');
-  assert.throws(
-    () => require(modulePath),
-    new Error(`Cannot find module '${modulePath}'`)
-  );
-  assert.throws(
-    () => require(modulePath + '.foo'),
-    new Error(`Cannot find module '${modulePath}.foo'`)
-  );
-}
-
-{
-  delete require.extensions['.bar'];
-  delete require.extensions['.foo.bar'];
-  const modulePath = path.join(tmpdir.path, 'test-extensions');
-  assert.throws(
-    () => require(modulePath),
-    new Error(`Cannot find module '${modulePath}'`)
-  );
-}
-
-{
-  delete require.extensions['.foo.bar'];
-  require.extensions['.bar'] = common.mustCall((module, path) => {
-    assert.strictEqual(module.id, file);
-    assert.strictEqual(path, file);
-  });
-
-  const modulePath = path.join(tmpdir.path, 'test-extensions.foo');
-  require(modulePath);
-}