diff --git a/types/ramda/index.d.ts b/types/ramda/index.d.ts
index aa84cad395..84d4edffce 100644
--- a/types/ramda/index.d.ts
+++ b/types/ramda/index.d.ts
@@ -15,7 +15,7 @@ declare namespace R {
     }
 
     interface Functor<T> {
-        map<T>(a: any): T;
+        map<U>(fn: (t: T) => U): Functor<U>;
     }
 
     interface ObjectIterator<T, TResult> {
diff --git a/types/ramda/ramda-tests.ts b/types/ramda/ramda-tests.ts
index 13aeb222f7..fa0c55d156 100644
--- a/types/ramda/ramda-tests.ts
+++ b/types/ramda/ramda-tests.ts
@@ -668,7 +668,7 @@ interface Obj { a: number; b: number };
     const stringFunctor = {
         map: (fn: (c: number) => number) => {
             var chars = "Ifmmp!Xpsme".split("");
-            return chars.map((char) => String.fromCharCode(fn(char.charCodeAt(0)))).join("");
+            return chars.map((char) => String.fromCharCode(fn(char.charCodeAt(0)))).join("") as any;
         }
     };
     R.map((x: number) => x-1, stringFunctor); // => "Hello World"
@@ -1985,3 +1985,10 @@ class Why {
     R.intersperse(0, [1, 2]); //=> [1, 0, 2]
     R.intersperse(0, [1]); //=> [1]
 }
+
+{
+    const functor = {
+        map: (fn: (x: string) => string) => functor
+    }
+    R.map(x => x.trim(), functor)
+}