diff --git a/.eslintrc.js b/.eslintrc.js
index 5f18b7e..4fe3cba 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -68,6 +68,9 @@ module.exports = {
     // Allow properties in ctors, as it reduces code duplicates
     '@typescript-eslint/no-parameter-properties': ['error', { allows: ['private readonly', 'protected readonly', 'public readonly'] }],
 
+    // You know what you're doing when you force-unwrap (dammit operator) an optional field
+    '@typescript-eslint/no-non-null-assertion': 'off',
+
     'eslint-comments/disable-enable-pair': ['error', { allowWholeFile: true }],
   },
   overrides: [
diff --git a/rollup.config.js b/rollup.config.js
index 993023d..31126ea 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -67,7 +67,7 @@ function buildOutput() {
 
       /* esm */
       {
-        file: `${ES5_BUNDLE_PATH}/index.esm${suffix}.js`,
+        file: `${ES5_BUNDLE_PATH}/index${suffix}.js`,
         format: 'es',
         sourcemap: true,
         plugins: [terser()],
diff --git a/src/impl/container-impl.spec.ts b/src/impl/container-impl.spec.ts
index b345943..08ad080 100644
--- a/src/impl/container-impl.spec.ts
+++ b/src/impl/container-impl.spec.ts
@@ -4,15 +4,19 @@ import * as assert from 'assert';
 import { Container, DependencyInjectionError } from '../interfaces';
 import { ContainerImpl } from './container-impl';
 import { createModernFactoryRegistry } from './create-modern-factory-registry';
+import { createLegacyFactoryRegistry } from './create-legacy-factory-registry';
 import { Cat, Dog, Fish, Meat, Milk, stringToken, symbolToken } from './container-types.spec';
 
-describe('ContainerImpl', () => {
-  // TODO: use legacyFactoryRegistry
-  describe('with ModernFactoryRegistry', () => {
+const testBlocks = [
+  { title: 'ContainerImpl with ModernFactoryRegistry', makeRegistry: createModernFactoryRegistry },
+  { title: 'ContainerImpl with LegacyFactoryRegistry', makeRegistry: createLegacyFactoryRegistry },
+];
+testBlocks.forEach(({ title, makeRegistry }) => {
+  describe(title, () => {
     let container: Container;
 
     beforeEach(() => {
-      container = new ContainerImpl(createModernFactoryRegistry());
+      container = new ContainerImpl(makeRegistry());
     });
 
     it('error path - no registration', () => {
diff --git a/src/impl/create-legacy-factory-registry.ts b/src/impl/create-legacy-factory-registry.ts
index 3da0c2c..636e84e 100644
--- a/src/impl/create-legacy-factory-registry.ts
+++ b/src/impl/create-legacy-factory-registry.ts
@@ -1,23 +1,28 @@
-import { FactoryRegistry } from '../interfaces';
+import { FactoryRegistry, ResolveFactoryFunction, Token } from '../interfaces';
 
 export function createLegacyFactoryRegistry(): FactoryRegistry {
-  const factoryByToken = Object.create(null);
+  // cannot use `string | symbol` type here, see https://github.com/Microsoft/TypeScript/issues/24587
+  const factoryByToken: Record<string, ResolveFactoryFunction<unknown>> = Object.create(null);
+  // cannot iterate through symbols as keys in ES5
+  const keys: Token<unknown>[] = [];
+
+  const toKey = (token: Token<unknown>) => token as unknown as string;
 
   return {
-    getTokens: () => {
-      throw Error('not impl');
-    },
-    hasFactory: (token) => {
-      throw Error('not impl');
-    },
-    getFactory: (token) => {
-      throw Error('not impl');
-    },
+    getTokens: () => keys,
+    hasFactory: (token) => Object.prototype.hasOwnProperty.call(factoryByToken, toKey(token)),
+    getFactory: (token) => factoryByToken[toKey(token)],
     setFactory(token, factory) {
-      throw Error('not impl');
+      if (!this.hasFactory(token)) {
+        keys.push(token);
+      }
+      factoryByToken[toKey(token)] = factory;
     },
     forEach(callback) {
-      throw Error('not impl');
+      keys.forEach((token) => {
+        const factory = this.getFactory(token)!;
+        callback(factory, token, this);
+      });
     },
   };
 }
diff --git a/src/interfaces/di-error.spec.ts b/src/interfaces/di-error.spec.ts
index fab45cf..1488996 100644
--- a/src/interfaces/di-error.spec.ts
+++ b/src/interfaces/di-error.spec.ts
@@ -1,4 +1,3 @@
-/* eslint-disable @typescript-eslint/no-non-null-assertion */
 import { describe, it } from 'mocha';
 import * as assert from 'assert';