diff --git a/.cursor/rules/architecture.mdc b/.cursor/rules/architecture.mdc
index 7588a85c1..d83fabffa 100644
--- a/.cursor/rules/architecture.mdc
+++ b/.cursor/rules/architecture.mdc
@@ -12,6 +12,6 @@ All core logic is written once as a `Generator` function (`function *`). Use `yi
 
 Never duplicate logic into separate async and sync methods. A single generator serves both paths.
 
-When wrapping an async+sync function pair (e.g. `contains`/`containsSync`, `exists`/`existsSync`, `readFile`/`readFileSync`), use `toLiquidAsync(syncFn, asyncFn?)` which returns a `LiquidAsync<F>` — one function that picks the sync or async implementation based on a leading `sync: boolean` arg. Then `yield` the result inside a generator to let the driver handle it in both modes.
+When wrapping an async+sync function pair (e.g. `contains`/`containsSync`, `exists`/`existsSync`, `readFile`/`readFileSync`), use `toLiquidAsync(asyncFn, syncFn?)` which returns a `LiquidAsync<F>` — one function that picks the sync or async implementation based on a leading `sync: boolean` arg. Then `yield` the result inside a generator to let the driver handle it in both modes.
 
 See `src/util/async.ts`.
diff --git a/src/fs/fs-impl.spec.ts b/src/fs/fs-impl.spec.ts
index ceb21d0cd..1258ca78e 100644
--- a/src/fs/fs-impl.spec.ts
+++ b/src/fs/fs-impl.spec.ts
@@ -1,9 +1,10 @@
 import * as fs from './fs-impl'
 import * as path from 'path'
 import { mkdtempSync, writeFileSync, symlinkSync, rmSync } from 'fs'
-const { join } = path
 import { tmpdir } from 'os'
 
+const { join } = path
+
 describe('fs-impl', function () {
   describe('.resolve()', function () {
     it('should resolve based on root', async function () {
@@ -54,7 +55,8 @@ describe('fs-impl', function () {
     })
   })
   describe('.contains()', () => {
-    it('should return false when path is a symlink to outside root', async () => {
+    const canSymlink = process.platform !== 'win32'
+    ;(canSymlink ? it : it.skip)('should return false when path is a symlink to outside root', async () => {
       const root = mkdtempSync(join(tmpdir(), 'liquid-contains-'))
       const outside = join(tmpdir(), `secret-${Date.now()}.liquid`)
       writeFileSync(outside, 'x')
@@ -69,7 +71,8 @@ describe('fs-impl', function () {
     })
   })
   describe('.containsSync()', () => {
-    it('should return false when path is a symlink to outside root', () => {
+    const canSymlink = process.platform !== 'win32'
+    ;(canSymlink ? it : it.skip)('should return false when path is a symlink to outside root', () => {
       const root = mkdtempSync(join(tmpdir(), 'liquid-contains-'))
       const outside = join(tmpdir(), `secret-${Date.now()}.liquid`)
       writeFileSync(outside, 'x')
diff --git a/src/fs/loader.spec.ts b/src/fs/loader.spec.ts
index 01414d503..81116b2d9 100644
--- a/src/fs/loader.spec.ts
+++ b/src/fs/loader.spec.ts
@@ -1,4 +1,5 @@
 import * as fs from './fs-impl'
+import { resolve } from 'path'
 import { Loader, LookupType } from './loader'
 import { toValueSync } from '../util/async'
 
@@ -7,7 +8,7 @@ describe('fs/loader', function () {
     it('should resolve relatively', function () {
       const loader = new Loader({ relativeReference: true, fs, extname: '' } as any)
       const candidates = [...loader.candidates('./foo/bar', ['/root', '/root/foo'], '/root/current')]
-      expect(candidates).toContain('/root/foo/bar')
+      expect(candidates).toContain(resolve('/root/foo/bar'))
     })
   })
   describe('.lookup()', function () {
@@ -27,7 +28,7 @@ describe('fs/loader', function () {
       const mockFs = { ...fs, existsSync: () => true, exists: async () => true, contains: undefined, containsSync: undefined }
       const loader = new Loader({ relativeReference: true, fs: mockFs, extname: '', partials: ['/root'] } as any)
       const result = toValueSync(loader.lookup('./foo/bar', LookupType.Partials, true, '/root/current'))
-      expect(result).toBe('/root/foo/bar')
+      expect(result).toBe(resolve('/root/foo/bar'))
     })
   })
 })
diff --git a/src/fs/loader.ts b/src/fs/loader.ts
index 4a42cd650..b0e471e11 100644
--- a/src/fs/loader.ts
+++ b/src/fs/loader.ts
@@ -32,12 +32,12 @@ export class Loader {
     }
     const fs = options.fs
     this.contains = toLiquidAsync(
-      fs.containsSync?.bind(fs) || (() => true),
-      fs.contains?.bind(fs)
+      fs.contains?.bind(fs) || (async () => true),
+      fs.containsSync?.bind(fs) || (() => true)
     )
     this.exists = toLiquidAsync(
-      fs.existsSync.bind(fs),
-      fs.exists.bind(fs)
+      fs.exists?.bind(fs) || (async () => false),
+      fs.existsSync?.bind(fs)
     )
   }
 
diff --git a/src/parser/parser.ts b/src/parser/parser.ts
index e55fabe7e..f61f2323e 100644
--- a/src/parser/parser.ts
+++ b/src/parser/parser.ts
@@ -26,8 +26,8 @@ export class Parser {
     this.loader = new Loader(this.liquid.options)
     this.parseLimit = new Limiter('parse length', liquid.options.parseLimit)
     this.readFile = toLiquidAsync(
-      this.fs.readFileSync.bind(this.fs),
-      this.fs.readFile.bind(this.fs)
+      this.fs.readFile?.bind(this.fs) || (async () => { throw new Error('readFile not implemented') }),
+      this.fs.readFileSync?.bind(this.fs)
     )
   }
   public parse (html: string, filepath?: string): Template[] {
diff --git a/src/util/async.ts b/src/util/async.ts
index d9018af6c..c190cd860 100644
--- a/src/util/async.ts
+++ b/src/util/async.ts
@@ -4,12 +4,12 @@ export type LiquidAsync<F extends (...args: any[]) => any> =
   (sync: boolean, ...args: Parameters<F>) => ReturnType<F> | Promise<ReturnType<F>>
 
 export function toLiquidAsync<F extends (...args: any[]) => any> (
-  syncFn: F,
-  asyncFn?: (...args: Parameters<F>) => Promise<ReturnType<F>>
+  asyncFn: (...args: Parameters<F>) => Promise<ReturnType<F>>,
+  syncFn?: F
 ): LiquidAsync<F> {
-  const asyncImpl = asyncFn || syncFn as any
+  const syncImpl = syncFn || asyncFn as any
   return (sync: boolean, ...args: any[]) => {
-    return sync ? syncFn(...args as Parameters<F>) : asyncImpl(...args as Parameters<F>)
+    return sync ? syncImpl(...args as Parameters<F>) : asyncFn(...args as Parameters<F>)
   }
 }
 
diff --git a/test/e2e/parse-and-render.spec.ts b/test/e2e/parse-and-render.spec.ts
index 3a88ad30c..cfca9c2b2 100644
--- a/test/e2e/parse-and-render.spec.ts
+++ b/test/e2e/parse-and-render.spec.ts
@@ -60,7 +60,8 @@ describe('.parseAndRender()', function () {
     const html = await engine.parseAndRender(src)
     expect(html).toBe('true')
   })
-  describe('symlink outside root', function () {
+  const canSymlink = process.platform !== 'win32'
+  ;(canSymlink ? describe : describe.skip)('symlink outside root', function () {
     let root: string, secret: string
     beforeAll(function () {
       root = mkdtempSync(join(tmpdir(), 'liquid-e2e-root-'))
diff --git a/test/stub/mockfs.ts b/test/stub/mockfs.ts
index 1428f14a6..4c9d4cea3 100644
--- a/test/stub/mockfs.ts
+++ b/test/stub/mockfs.ts
@@ -1,6 +1,6 @@
 import { isString, forOwn } from '../../src/util/underscore'
 import * as fs from '../../src/fs/fs-impl'
-import { resolve } from 'path'
+import { resolve, sep } from 'path'
 
 interface FileDescriptor {
   mode: string;
@@ -33,12 +33,12 @@ export function mock (options: { [path: string]: (string | FileDescriptor) }) {
   };
   (fs as any).contains = async (root: string, file: string) => {
     root = resolve(root)
-    if (!root.endsWith('/')) root += '/'
+    if (!root.endsWith(sep)) root += sep
     return file.startsWith(root)
   };
   (fs as any).containsSync = (root: string, file: string) => {
     root = resolve(root)
-    if (!root.endsWith('/')) root += '/'
+    if (!root.endsWith(sep)) root += sep
     return file.startsWith(root)
   }
 }