diff --git a/packages/auth-adapters/better-auth/src/adapter.ts b/packages/auth-adapters/better-auth/src/adapter.ts
index 27b2d4f59..3221f6952 100644
--- a/packages/auth-adapters/better-auth/src/adapter.ts
+++ b/packages/auth-adapters/better-auth/src/adapter.ts
@@ -187,7 +187,9 @@ export const zenstackAdapter = <Schema extends SchemaDef>(db: ClientContract<Sch
                 options: config,
 
                 createSchema: async ({ file, tables }) => {
-                    const generateSchema = (await import('./schema-generator')).generateSchema;
+                    // Self-import via package subpath (not a relative './schema-generator') so the
+                    // bundler treats it as external and keeps it lazy in the CJS output — see tsdown.config.ts.
+                    const generateSchema = (await import('@zenstackhq/better-auth/schema-generator')).generateSchema;
                     return generateSchema(file, tables, config, options);
                 },
             };
diff --git a/packages/auth-adapters/better-auth/tsconfig.json b/packages/auth-adapters/better-auth/tsconfig.json
index 3c7378e93..0cecd4cdc 100644
--- a/packages/auth-adapters/better-auth/tsconfig.json
+++ b/packages/auth-adapters/better-auth/tsconfig.json
@@ -3,7 +3,10 @@
     "compilerOptions": {
         "rootDir": ".",
         "noPropertyAccessFromIndexSignature": false,
-        "types": ["node"]
+        "types": ["node"],
+        "paths": {
+            "@zenstackhq/better-auth/schema-generator": ["./src/schema-generator.ts"]
+        }
     },
     "include": ["src/**/*"]
 }
diff --git a/packages/auth-adapters/better-auth/tsdown.config.ts b/packages/auth-adapters/better-auth/tsdown.config.ts
index 28af6aa31..075a684a2 100644
--- a/packages/auth-adapters/better-auth/tsdown.config.ts
+++ b/packages/auth-adapters/better-auth/tsdown.config.ts
@@ -1,3 +1,18 @@
 import { createConfig } from '@zenstackhq/tsdown-config';
 
-export default createConfig({ entry: { index: 'src/index.ts', 'schema-generator': 'src/schema-generator.ts' } });
+// `index` and `schema-generator` are built as two separate tsdown invocations so that
+// the lazy `await import('@zenstackhq/better-auth/schema-generator')` in the adapter
+// stays lazy in the CJS output. When both entries live in a single build, Rolldown
+// treats them as siblings and injects a top-level `require('./schema-generator.cjs')`
+// into `index.cjs`, which eagerly pulls in `@zenstackhq/language` (Langium) at adapter
+// load time. Splitting the builds hides that relationship; `neverBundle` then keeps
+// the dynamic import as a package-name reference that Node resolves at first call.
+export default [
+    createConfig({
+        entry: { index: 'src/index.ts' },
+        deps: { neverBundle: ['@zenstackhq/better-auth/schema-generator'] },
+    }),
+    createConfig({
+        entry: { 'schema-generator': 'src/schema-generator.ts' },
+    }),
+];