diff --git a/src/libstd/map.rs b/src/libstd/map.rs
index d6feebc016c8..041346c9cd9c 100644
--- a/src/libstd/map.rs
+++ b/src/libstd/map.rs
@@ -773,4 +773,25 @@ mod tests {
         assert map.get(~"b") == 2;
         assert map.get(~"c") == 3;
     }
+
+    #[test]
+    fn test_insert_with_key() {
+        let map = map::HashMap::<~str, uint>();
+
+        fn inc(k: ~str, v0: uint, v1: uint) -> uint {
+            v0 + v1
+        }
+
+        map.insert_with_key(inc, ~"cat", 1);
+        map.insert_with_key(inc, ~"mongoose", 1);
+        map.insert_with_key(inc, ~"cat", 7);
+        map.insert_with_key(inc, ~"ferret", 3);
+        map.insert_with_key(inc, ~"cat", 2);
+
+        assert 10 == option::get(map.find(~"cat"));
+        assert  3 == option::get(map.find(~"ferret"));
+        assert  1 == option::get(map.find(~"mongoose"));
+
+        assert None == map.find(~"unicorn");
+    }
 }
diff --git a/src/test/bench/shootout-k-nucleotide-pipes.rs b/src/test/bench/shootout-k-nucleotide-pipes.rs
index bf94e11980a6..42198a6d7896 100644
--- a/src/test/bench/shootout-k-nucleotide-pipes.rs
+++ b/src/test/bench/shootout-k-nucleotide-pipes.rs
@@ -69,10 +69,7 @@ fn find(mm: HashMap<~[u8], uint>, key: ~str) -> uint {
 // given a map, increment the counter for a key
 fn update_freq(mm: HashMap<~[u8], uint>, key: &[u8]) {
     let key = vec::slice(key, 0, key.len());
-    match mm.find(key) {
-      option::None      => { mm.insert(key, 1u      ); }
-      option::Some(val) => { mm.insert(key, 1u + val); }
-    }
+    mm.insert_with_key(|k,v,v1| {v + v1}, key, 1);
 }
 
 // given a ~[u8], for each window call a function
diff --git a/src/test/bench/shootout-k-nucleotide.rs b/src/test/bench/shootout-k-nucleotide.rs
index 9bc7abfdff78..f582ac6737df 100644
--- a/src/test/bench/shootout-k-nucleotide.rs
+++ b/src/test/bench/shootout-k-nucleotide.rs
@@ -66,10 +66,7 @@ fn find(mm: HashMap<~[u8], uint>, key: ~str) -> uint {
 // given a map, increment the counter for a key
 fn update_freq(mm: HashMap<~[u8], uint>, key: &[u8]) {
     let key = vec::slice(key, 0, key.len());
-    match mm.find(key) {
-      option::None      => { mm.insert(key, 1u      ); }
-      option::Some(val) => { mm.insert(key, 1u + val); }
-    }
+    mm.insert_with_key(|k,v,v1| {v + v1}, key, 1);
 }
 
 // given a ~[u8], for each window call a function