diff --git a/CHANGELOG.md b/CHANGELOG.md
index bfe46f09..4ee476b8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,11 @@
 **Note**: Gaps between patch versions are faulty/broken releases.
 **Note**: A feature tagged as Experimental is in a high state of flux, you're at risk of it changing without notice.
 
+# 2.2.22
+
+- **Bug Fix**
+  - Test for readonly type when optimizing tagged unions, #719
+
 # 2.2.21
 
 - **Bug Fix**
diff --git a/package-lock.json b/package-lock.json
index 874a36cf..f888869e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "io-ts",
-  "version": "2.2.20",
+  "version": "2.2.22",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "io-ts",
-      "version": "2.2.20",
+      "version": "2.2.22",
       "license": "MIT",
       "devDependencies": {
         "@definitelytyped/dtslint": "^0.0.163",
diff --git a/package.json b/package.json
index 265d1034..20650f72 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "io-ts",
-  "version": "2.2.21",
+  "version": "2.2.22",
   "description": "TypeScript runtime type system for IO decoding/encoding",
   "main": "lib/index.js",
   "module": "es6/index.js",
diff --git a/test/2.1.x/union.ts b/test/2.1.x/union.ts
index 44975d07..bcdf8ba7 100644
--- a/test/2.1.x/union.ts
+++ b/test/2.1.x/union.ts
@@ -238,6 +238,15 @@ describe.concurrent('union', () => {
         }
       )
     })
+
+    it('readonly', () => {
+      assert.strictEqual(t.getTags(t.readonly(t.strict({ a: t.string }))), t.emptyTags)
+      assert.deepStrictEqual(t.getTags(t.readonly(t.strict({ tag: t.literal('a') }))), { tag: ['a'] })
+      assert.deepStrictEqual(t.getTags(t.readonly(t.strict({ tag: t.literal('a'), type: t.literal('b') }))), {
+        tag: ['a'],
+        type: ['b']
+      })
+    })
   })
 
   it('getIndex', () => {