diff --git a/README.md b/README.md
index 1b4ca21..c44620e 100644
--- a/README.md
+++ b/README.md
@@ -181,7 +181,7 @@ Disables advanced emulation that relies on returning a `RegExp` subclass, result
 
 ### `flags`
 
-Oniguruma flags; a string with `i`, `m`, and `x` in any order (all optional).
+Oniguruma flags; a string with `i`, `m`, `x`, and `W` in any order (all optional).
 
 Flags can also be specified via modifiers in the pattern.
 
diff --git a/src/options.js b/src/options.js
index 6678ef7..85794c7 100644
--- a/src/options.js
+++ b/src/options.js
@@ -35,8 +35,8 @@ function getOptions(options) {
     // Disables advanced emulation that relies on returning a `RegExp` subclass, resulting in
     // certain patterns not being emulatable.
     avoidSubclass: false,
-    // Oniguruma flags; a string with `i`, `m`, and `x` in any order (all optional). Oniguruma's
-    // `m` is equivalent to JavaScript's `s` (`dotAll`).
+    // Oniguruma flags; a string with `i`, `m`, `x`, and `W` in any order (all optional).
+    // Oniguruma's `m` is equivalent to JavaScript's `s` (`dotAll`).
     flags: '',
     // Include JavaScript flag `g` (`global`) in the result.
     global: false,