diff --git a/.changeset/clever-clocks-yell.md b/.changeset/clever-clocks-yell.md
new file mode 100644
index 000000000..e32253110
--- /dev/null
+++ b/.changeset/clever-clocks-yell.md
@@ -0,0 +1,5 @@
+---
+'@emotion/unitless': minor
+---
+
+Source code has been migrated to TypeScript. From now on type declarations will be emitted based on that, instead of being hand-written.
diff --git a/packages/unitless/package.json b/packages/unitless/package.json
index f2639670a..2666a94f2 100644
--- a/packages/unitless/package.json
+++ b/packages/unitless/package.json
@@ -4,6 +4,7 @@
   "description": "An object of css properties that don't accept values with units",
   "main": "dist/emotion-unitless.cjs.js",
   "module": "dist/emotion-unitless.esm.js",
+  "types": "dist/emotion-unitless.cjs.d.ts",
   "license": "MIT",
   "repository": "https://github.com/emotion-js/emotion/tree/main/packages/unitless",
   "scripts": {
diff --git a/packages/unitless/src/index.js b/packages/unitless/src/index.ts
similarity index 94%
rename from packages/unitless/src/index.js
rename to packages/unitless/src/index.ts
index 797533b59..4f1aef669 100644
--- a/packages/unitless/src/index.js
+++ b/packages/unitless/src/index.ts
@@ -1,4 +1,4 @@
-let unitlessKeys /*: { [key: string]: 1 } */ = {
+let unitlessKeys = {
   animationIterationCount: 1,
   borderImageOutset: 1,
   borderImageSlice: 1,
@@ -46,6 +46,6 @@ let unitlessKeys /*: { [key: string]: 1 } */ = {
   strokeMiterlimit: 1,
   strokeOpacity: 1,
   strokeWidth: 1
-}
+} as const
 
 export default unitlessKeys