diff --git a/map/map.mbt b/map/map.mbt
index a57ac56c3..ffbb73aa6 100644
--- a/map/map.mbt
+++ b/map/map.mbt
@@ -167,6 +167,42 @@ pub fn iter[K : Compare, V](self : Map[K, V], f : (K, V) -> Unit) -> Unit {
   }
 }
 
+/// Iterate over the key-value pairs with index.
+pub fn iteri[K, V](self : Map[K, V], f : (Int, K, V) -> Unit) -> Unit {
+  fn do_iteri(m : Map[K, V], f, i) {
+    match m {
+      Empty => ()
+      Tree(k, v, _, l, r) => {
+        do_iteri(l, f, i)
+        f(size(l) + i, k, v)
+        do_iteri(r, f, size(l) + i + 1)
+      }
+    }
+  }
+
+  do_iteri(self, f, 0)
+}
+
+/// Maps over the values in the map.
+pub fn map[K , X, Y](self : Map[K, X], f : (X) -> Y) -> Map[K, Y] {
+  match self {
+    Empty => Empty
+    Tree(k, v, s, l, r) => Tree(k, f(v), s, map(l, f), map(r, f))
+  }
+}
+
+/// Maps over the key-value pairs in the map.
+pub fn map_with_key[K , X, Y](
+  self : Map[K, X],
+  f : (K, X) -> Y
+) -> Map[K, Y] {
+  match self {
+    Empty => Empty
+    Tree(k, v, s, l, r) =>
+      Tree(k, f(k, v), s, map_with_key(l, f), map_with_key(r, f))
+  }
+}
+
 /// The ratio between the sizes of the left and right subtrees.
 let ratio = 5
 
@@ -339,6 +375,31 @@ test "iter" {
   @assertion.assert_eq(s, "(0,zero)(1,one)(2,two)(3,three)(8,eight)")?
 }
 
+test "iteri" {
+  let m = Map::[(3, "three"), (8, "eight"), (1, "one"), (2, "two"), (0, "zero")]
+  let mut s = ""
+  m.iteri(fn(i, k, v) { s = s + "(\(i),\(k),\(v))" })
+  @assertion.assert_eq(s, "(0,0,zero)(1,1,one)(2,2,two)(3,3,three)(4,8,eight)")?
+}
+
+test "map" {
+  let m = Map::[(3, "three"), (8, "eight"), (1, "one"), (2, "two"), (0, "zero")]
+  let n = m.map(fn(v) { v + "X" })
+  @assertion.assert_eq(
+    n.debug_tree(),
+    "(3,threeX,(1,oneX,(0,zeroX,_,_),(2,twoX,_,_)),(8,eightX,_,_))",
+  )?
+}
+
+test "map_with_key" {
+  let m = Map::[(3, "three"), (8, "eight"), (1, "one"), (2, "two"), (0, "zero")]
+  let n = m.map_with_key(fn(k, v) { "\(k)-\(v)" })
+  @assertion.assert_eq(
+    n.debug_tree(),
+    "(3,3-three,(1,1-one,(0,0-zero,_,_),(2,2-two,_,_)),(8,8-eight,_,_))",
+  )?
+}
+
 test "singleton" {
   let m = singleton(3, "three")
   @assertion.assert_eq(m.debug_tree(), "(3,three,_,_)")?