diff --git a/packages/agent/package.json b/packages/agent/package.json
index 7edb2c9..79b0db3 100644
--- a/packages/agent/package.json
+++ b/packages/agent/package.json
@@ -8,7 +8,6 @@
   "types": "index.d.ts",
   "exports": {
     ".": {
-      "source": "./src/index.ts",
       "types": "./index.d.ts",
       "import": "./esm/index.js",
       "require": "./index.js"
@@ -31,6 +30,7 @@
     "clean": "makage clean",
     "prepack": "npm run build",
     "build": "makage build",
+    "postbuild": "node ../../scripts/write-esm-package-json.js",
     "build:dev": "makage build --dev",
     "lint": "eslint . --fix",
     "test": "jest",
diff --git a/packages/agentic-kit/package.json b/packages/agentic-kit/package.json
index 93b0b2a..b208b7d 100644
--- a/packages/agentic-kit/package.json
+++ b/packages/agentic-kit/package.json
@@ -8,7 +8,6 @@
   "types": "index.d.ts",
   "exports": {
     ".": {
-      "source": "./src/index.ts",
       "types": "./index.d.ts",
       "import": "./esm/index.js",
       "require": "./index.js"
@@ -31,6 +30,7 @@
     "clean": "makage clean",
     "prepack": "npm run build",
     "build": "makage build",
+    "postbuild": "node ../../scripts/write-esm-package-json.js",
     "build:dev": "makage build --dev",
     "lint": "eslint . --fix",
     "test": "jest",
diff --git a/packages/anthropic/package.json b/packages/anthropic/package.json
index 1512594..4692b79 100644
--- a/packages/anthropic/package.json
+++ b/packages/anthropic/package.json
@@ -8,7 +8,6 @@
   "types": "index.d.ts",
   "exports": {
     ".": {
-      "source": "./src/index.ts",
       "types": "./index.d.ts",
       "import": "./esm/index.js",
       "require": "./index.js"
@@ -31,6 +30,7 @@
     "clean": "makage clean",
     "prepack": "npm run build",
     "build": "makage build",
+    "postbuild": "node ../../scripts/write-esm-package-json.js",
     "build:dev": "makage build --dev",
     "lint": "eslint . --fix",
     "test": "jest",
diff --git a/packages/ollama/package.json b/packages/ollama/package.json
index ec3c939..756cf1a 100644
--- a/packages/ollama/package.json
+++ b/packages/ollama/package.json
@@ -8,7 +8,6 @@
   "types": "index.d.ts",
   "exports": {
     ".": {
-      "source": "./src/index.ts",
       "types": "./index.d.ts",
       "import": "./esm/index.js",
       "require": "./index.js"
@@ -31,6 +30,7 @@
     "clean": "makage clean",
     "prepack": "npm run build",
     "build": "makage build",
+    "postbuild": "node ../../scripts/write-esm-package-json.js",
     "build:dev": "makage build --dev",
     "lint": "eslint . --fix",
     "test": "jest",
diff --git a/packages/openai/package.json b/packages/openai/package.json
index 70e597c..6082398 100644
--- a/packages/openai/package.json
+++ b/packages/openai/package.json
@@ -8,7 +8,6 @@
   "types": "index.d.ts",
   "exports": {
     ".": {
-      "source": "./src/index.ts",
       "types": "./index.d.ts",
       "import": "./esm/index.js",
       "require": "./index.js"
@@ -31,6 +30,7 @@
     "clean": "makage clean",
     "prepack": "npm run build",
     "build": "makage build",
+    "postbuild": "node ../../scripts/write-esm-package-json.js",
     "build:dev": "makage build --dev",
     "lint": "eslint . --fix",
     "test": "jest",
diff --git a/packages/react/package.json b/packages/react/package.json
index 79c8b5d..5823340 100644
--- a/packages/react/package.json
+++ b/packages/react/package.json
@@ -8,7 +8,6 @@
   "types": "index.d.ts",
   "exports": {
     ".": {
-      "source": "./src/index.ts",
       "types": "./index.d.ts",
       "import": "./esm/index.js",
       "require": "./index.js"
@@ -31,6 +30,7 @@
     "clean": "makage clean",
     "prepack": "npm run build",
     "build": "makage build",
+    "postbuild": "node ../../scripts/write-esm-package-json.js",
     "build:dev": "makage build --dev",
     "lint": "eslint . --fix",
     "test": "jest",
diff --git a/scripts/write-esm-package-json.js b/scripts/write-esm-package-json.js
new file mode 100644
index 0000000..f402323
--- /dev/null
+++ b/scripts/write-esm-package-json.js
@@ -0,0 +1,11 @@
+#!/usr/bin/env node
+// Writes dist/esm/package.json with {"type":"module"} so Node treats the
+// ESM build's .js files as modules. Runs from each package's cwd as a
+// postbuild step.
+
+const fs = require('node:fs');
+const path = require('node:path');
+
+const target = path.join('dist', 'esm', 'package.json');
+fs.mkdirSync(path.dirname(target), { recursive: true });
+fs.writeFileSync(target, '{"type":"module"}\n');