diff --git a/src/function.js b/src/function.js
index f4ef437..c00f94f 100644
--- a/src/function.js
+++ b/src/function.js
@@ -116,7 +116,7 @@ export const ap = curry(dispatch(['fantasy-land/ap', 'ap'],
   /**
     * @template A, B
     * @template {Morphism<A, B>} Ap
-    * @param {Morphism<A, B>} f 
+    * @param {Ap} f 
     * @param {{ ap: Ap } | Ap} a
     */
   (f, a) => {
@@ -131,7 +131,7 @@ export const ap = curry(dispatch(['fantasy-land/ap', 'ap'],
   }))
 
 export const chain = curry(dispatch(['fantasy-land/chain', 'chain'],
-  (f, a) => a.map(f)
+  (f, a) => f(a)
 ))
 
 export const map = curry(dispatch(['fantasy-land/map', 'map'],