diff --git a/.changeset/quiet-crews-leave.md b/.changeset/quiet-crews-leave.md
new file mode 100644
index 0000000000000..9780f99ca98b8
--- /dev/null
+++ b/.changeset/quiet-crews-leave.md
@@ -0,0 +1,5 @@
+---
+'@eth-optimism/atst': minor
+---
+
+Fix main and module in atst package.json
diff --git a/packages/atst/package.json b/packages/atst/package.json
index cb0cd16020902..70b2bc38851af 100644
--- a/packages/atst/package.json
+++ b/packages/atst/package.json
@@ -2,9 +2,9 @@
   "name": "@eth-optimism/atst",
   "version": "0.1.0",
   "type": "module",
-  "main": "dist/index.js",
+  "main": "dist/index.cjs",
   "types": "src/index.ts",
-  "module": "dist/index.cjs",
+  "module": "dist/index.js",
   "license": "MIT",
   "exports": {
     ".": {