diff --git a/serde/src/lib.rs b/serde/src/lib.rs
index 58cc9b8f..467a2266 100644
--- a/serde/src/lib.rs
+++ b/serde/src/lib.rs
@@ -61,7 +61,7 @@
 
 #![doc(html_root_url="https://docs.serde.rs")]
 #![cfg_attr(not(feature = "std"), no_std)]
-#![cfg_attr(feature = "unstable", feature(nonzero, inclusive_range, zero_one))]
+#![cfg_attr(feature = "unstable", feature(inclusive_range, nonzero, specialization, zero_one))]
 #![cfg_attr(feature = "alloc", feature(alloc))]
 #![cfg_attr(feature = "collections", feature(collections))]
 #![cfg_attr(feature = "cargo-clippy", allow(linkedlist, type_complexity, doc_markdown))]
diff --git a/serde/src/ser/impls.rs b/serde/src/ser/impls.rs
index c23afdbc..f2fbb37d 100644
--- a/serde/src/ser/impls.rs
+++ b/serde/src/ser/impls.rs
@@ -66,9 +66,6 @@ use super::{
 #[cfg(any(feature = "std", feature = "unstable"))]
 use super::Error;
 
-#[cfg(feature = "unstable")]
-use super::Iterator;
-
 ///////////////////////////////////////////////////////////////////////////////
 
 macro_rules! impl_visit {
@@ -147,24 +144,6 @@ impl<T> Serialize for PhantomData<T> {
     }
 }
 
-
-///////////////////////////////////////////////////////////////////////////////
-
-impl<T> Serialize for [T]
-    where T: Serialize,
-{
-    #[inline]
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-        where S: Serializer,
-    {
-        let mut seq = try!(serializer.serialize_seq(Some(self.len())));
-        for e in self {
-            try!(seq.serialize_element(e));
-        }
-        seq.end()
-    }
-}
-
 ///////////////////////////////////////////////////////////////////////////////
 
 macro_rules! array_impls {
@@ -220,33 +199,7 @@ array_impls!(32);
 
 ///////////////////////////////////////////////////////////////////////////////
 
-#[cfg(feature = "unstable")]
-impl<'a, I> Serialize for Iterator<I>
-    where I: IntoIterator, <I as IntoIterator>::Item: Serialize
-{
-    #[inline]
-    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
-        where S: Serializer,
-    {
-        // FIXME: use specialization to prevent invalidating the object in case of clonable iterators?
-        let iter = match self.data.borrow_mut().take() {
-            Some(iter) => iter.into_iter(),
-            None => return Err(Error::custom("Iterator used twice")),
-        };
-        let size = match iter.size_hint() {
-            (lo, Some(hi)) if lo == hi => Some(lo),
-            _ => None,
-        };
-        let mut seq = try!(serializer.serialize_seq(size));
-        for e in iter {
-            try!(seq.serialize_element(&e));
-        }
-        seq.end()
-    }
-}
-
-///////////////////////////////////////////////////////////////////////////////
-
+#[cfg(not(feature = "unstable"))]
 macro_rules! serialize_seq {
     () => {
         #[inline]
@@ -262,6 +215,24 @@ macro_rules! serialize_seq {
     }
 }
 
+#[cfg(feature = "unstable")]
+macro_rules! serialize_seq {
+    () => {
+        #[inline]
+        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            where S: Serializer,
+        {
+            serializer.collect_seq(self)
+        }
+    }
+}
+
+impl<T> Serialize for [T]
+    where T: Serialize,
+{
+    serialize_seq!();
+}
+
 #[cfg(any(feature = "std", feature = "collections"))]
 impl<T> Serialize for BinaryHeap<T>
     where T: Serialize + Ord
@@ -550,6 +521,7 @@ tuple_impls! {
 
 ///////////////////////////////////////////////////////////////////////////////
 
+#[cfg(not(feature = "unstable"))]
 macro_rules! serialize_map {
     () => {
         #[inline]
@@ -566,6 +538,18 @@ macro_rules! serialize_map {
     }
 }
 
+#[cfg(feature = "unstable")]
+macro_rules! serialize_map {
+    () => {
+        #[inline]
+        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            where S: Serializer,
+        {
+            serializer.collect_map(self)
+        }
+    }
+}
+
 #[cfg(any(feature = "std", feature = "collections"))]
 impl<K, V> Serialize for BTreeMap<K, V>
     where K: Serialize + Ord,
diff --git a/serde/src/ser/mod.rs b/serde/src/ser/mod.rs
index 42ccd169..331928a3 100644
--- a/serde/src/ser/mod.rs
+++ b/serde/src/ser/mod.rs
@@ -98,10 +98,8 @@ use std::error;
 #[cfg(not(feature = "std"))]
 use error;
 
-#[cfg(feature = "unstable")]
-use core::cell::RefCell;
-
 use core::fmt::Display;
+use core::iter::IntoIterator;
 
 mod impls;
 mod impossible;
@@ -242,7 +240,7 @@ pub trait Serialize {
 /// is the `serde_json::value::Serializer` (distinct from the main `serde_json`
 /// serializer) that produces a `serde_json::Value` data structure in memory as
 /// output.
-pub trait Serializer {
+pub trait Serializer: Sized {
     /// The output type produced by this `Serializer` during successful
     /// serialization. Most serializers that produce text or binary output
     /// should set `Ok = ()` and serialize into an `io::Write` or buffer
@@ -607,6 +605,41 @@ pub trait Serializer {
         variant: &'static str,
         len: usize,
     ) -> Result<Self::SerializeStructVariant, Self::Error>;
+
+    /// Collect an iterator as a sequence.
+    ///
+    /// The default implementation serializes each item yielded by the iterator
+    /// using `Self::SerializeSeq`. Implementors should not need to override
+    /// this method.
+    fn collect_seq<I>(self, iter: I) -> Result<Self::Ok, Self::Error>
+        where I: IntoIterator,
+              <I as IntoIterator>::Item: Serialize,
+    {
+        let iter = iter.into_iter();
+        let mut serializer = try!(self.serialize_seq(iter.len_hint()));
+        for item in iter {
+            try!(serializer.serialize_element(&item));
+        }
+        serializer.end()
+    }
+
+    /// Collect an iterator as a map.
+    ///
+    /// The default implementation serializes each pair yielded by the iterator
+    /// using `Self::SerializeMap`. Implementors should not need to override
+    /// this method.
+    fn collect_map<K, V, I>(self, iter: I) -> Result<Self::Ok, Self::Error>
+        where K: Serialize,
+              V: Serialize,
+              I: IntoIterator<Item = (K, V)>,
+    {
+        let iter = iter.into_iter();
+        let mut serializer = try!(self.serialize_map(iter.len_hint()));
+        for (key, value) in iter {
+            try!(serializer.serialize_entry(&key, &value));
+        }
+        serializer.end()
+    }
 }
 
 /// Returned from `Serializer::serialize_seq` and
@@ -803,26 +836,32 @@ pub trait SerializeStructVariant {
     fn end(self) -> Result<Self::Ok, Self::Error>;
 }
 
-/// A wrapper type for iterators that implements `Serialize` for iterators whose
-/// items implement `Serialize`. Don't use multiple times. Create new versions
-/// of this with the `serde::ser::iterator` function every time you want to
-/// serialize an iterator.
-#[cfg(feature = "unstable")]
-pub struct Iterator<I>
-    where <I as IntoIterator>::Item: Serialize,
-          I: IntoIterator
-{
-    data: RefCell<Option<I>>,
+trait LenHint: Iterator {
+    fn len_hint(&self) -> Option<usize>;
 }
 
-/// Create a wrapper type that can be passed to any function expecting a
-/// `Serialize` and will serialize the given iterator as a sequence.
-#[cfg(feature = "unstable")]
-pub fn iterator<I>(iter: I) -> Iterator<I>
-    where <I as IntoIterator>::Item: Serialize,
-          I: IntoIterator
-{
-    Iterator {
-        data: RefCell::new(Some(iter)),
+impl<I: Iterator> LenHint for I {
+    #[cfg(not(feature = "unstable"))]
+    fn len_hint(&self) -> Option<usize> {
+        iterator_len_hint(self)
+    }
+
+    #[cfg(feature = "unstable")]
+    default fn len_hint(&self) -> Option<usize> {
+        iterator_len_hint(self)
+    }
+}
+
+#[cfg(feature = "unstable")]
+impl<I: ExactSizeIterator> LenHint for I {
+    fn len_hint(&self) -> Option<usize> {
+        Some(self.len())
+    }
+}
+
+fn iterator_len_hint<I: Iterator>(iter: &I) -> Option<usize> {
+    match iter.size_hint() {
+        (lo, Some(hi)) if lo == hi => Some(lo),
+        _ => None,
     }
 }