diff --git a/src/libcollections/dlist.rs b/src/libcollections/dlist.rs
index d50b212c7dd..f49a0c037de 100644
--- a/src/libcollections/dlist.rs
+++ b/src/libcollections/dlist.rs
@@ -351,18 +351,16 @@ impl<T> DList<T> {
     ///     println!("{}", e); // prints 2, then 4, then 11, then 7, then 8
     /// }
     /// ```
-    pub fn insert_when(&mut self, elt: T, f: |&T, &T| -> bool) {
-        {
-            let mut it = self.iter_mut();
-            loop {
-                match it.peek_next() {
-                    None => break,
-                    Some(x) => if f(x, &elt) { break }
-                }
-                it.next();
+    pub fn insert_when<F>(&mut self, elt: T, mut f: F) where F: FnMut(&T, &T) -> bool {
+        let mut it = self.iter_mut();
+        loop {
+            match it.peek_next() {
+                None => break,
+                Some(x) => if f(x, &elt) { break }
             }
-            it.insert_next(elt);
+            it.next();
         }
+        it.insert_next(elt);
     }
 
     /// Merges `other` into this `DList`, using the function `f`.
@@ -371,7 +369,7 @@ impl<T> DList<T> {
     /// put `a` in the result if `f(a, b)` is true, and otherwise `b`.
     ///
     /// This operation should compute in O(max(N, M)) time.
-    pub fn merge(&mut self, mut other: DList<T>, f: |&T, &T| -> bool) {
+    pub fn merge<F>(&mut self, mut other: DList<T>, mut f: F) where F: FnMut(&T, &T) -> bool {
         {
             let mut it = self.iter_mut();
             loop {