diff --git a/index.js b/index.js
index d31d469..6e75ce2 100644
--- a/index.js
+++ b/index.js
@@ -14,24 +14,10 @@ const defaults = {behavior: 'prepend', content: contentDefaults}
 
 const splice = [].splice
 
-let deprecationWarningIssued = false
-
 export default function attacher(options = {}) {
   let {linkProperties, behavior, content, group} = {...defaults, ...options}
   let method
 
-  // NOTE: Remove in next major version
-  if (options.behaviour !== undefined) {
-    if (!deprecationWarningIssued) {
-      deprecationWarningIssued = true
-      console.warn(
-        '[remark-autolink-headings] Deprecation Warning: `behaviour` is a nonstandard option. Use `behavior` instead.'
-      )
-    }
-
-    behavior = options.behaviour
-  }
-
   if (behavior === 'wrap') {
     method = wrap
   } else if (behavior === 'before' || behavior === 'after') {
diff --git a/test/index.js b/test/index.js
index f540702..6993cd2 100644
--- a/test/index.js
+++ b/test/index.js
@@ -24,17 +24,6 @@ test('remarkAutolinkHeadings', (t) => {
       base('output.' + b + '.html'),
       'should autolink headings (' + b + ')'
     )
-
-    t.is(
-      remark()
-        .use(remarkSlug)
-        .use(remarkHtml)
-        .use(remarkAutolinkHeadings, {behaviour: b})
-        .processSync(base('input.md'))
-        .toString(),
-      base('output.' + b + '.html'),
-      'should autolink headings with deprecated option (' + b + ')'
-    )
   }
 
   t.is(
@@ -98,7 +87,7 @@ test('remarkAutolinkHeadings', (t) => {
           tagName: 'div',
           properties: {className: ['heading-group']}
         },
-        behaviour: 'before'
+        behavior: 'before'
       })
       .processSync('# method')
       .toString(),
@@ -117,7 +106,7 @@ test('remarkAutolinkHeadings', (t) => {
             properties: {className: ['heading-' + node.depth + '-group']}
           }
         },
-        behaviour: 'after'
+        behavior: 'after'
       })
       .processSync('# method')
       .toString(),