diff --git a/README.md b/README.md
index addf5ed..057c65e 100755
--- a/README.md
+++ b/README.md
@@ -59,12 +59,16 @@ When using the ESM version, Wasm is supported instead:
 
 ```js
 import { parse, init } from 'cjs-module-lexer';
-// init() needs to be called and waited upon, or use initSync() to compile
-// Wasm blockingly and synchronously.
+// In browsers, initialize the Wasm before parsing.
 await init();
 const { exports, reexports } = parse(source);
 ```
 
+`parse` calls `initSync()` on first use if initialization has not completed.
+Call `initSync()` directly to choose when the blocking initialization runs.
+Browser main threads can restrict synchronous Wasm compilation, so await
+`init()` before parsing in browsers.
+
 The Wasm build is around 1.5x faster and without a cold start.
 
 ### Grammar
diff --git a/src/lexer.js b/src/lexer.js
index 30bca50..50e1961 100755
--- a/src/lexer.js
+++ b/src/lexer.js
@@ -4,7 +4,7 @@ const isLE = new Uint8Array(new Uint16Array([1]).buffer)[0] === 1;
 
 export function parse (source, name = '@') {
   if (!wasm)
-    throw new Error('Not initialized');
+    initSync();
 
   const len = source.length + 1;
 
diff --git a/test/_unit.js b/test/_unit.js
index 0458f17..391d95e 100755
--- a/test/_unit.js
+++ b/test/_unit.js
@@ -20,6 +20,16 @@ async function loadParser () {
 suite('Lexer', () => {
   suiteSetup(async () => await loadParser());
 
+  test('automatic Wasm initialization', async () => {
+    const lexer = await import('../dist/lexer.mjs?automatic-initialization');
+
+    assert.deepStrictEqual(lexer.parse('exports.value = 1'), {
+      exports: ['value'],
+      reexports: []
+    });
+    lexer.initSync();
+  });
+
   test('export star failure', () => {
     parse(`__exportStar((0));`);
   });