diff --git a/src/future/future/mod.rs b/src/future/future/mod.rs
index a913f4fc1..46780f8cf 100644
--- a/src/future/future/mod.rs
+++ b/src/future/future/mod.rs
@@ -45,7 +45,7 @@ extension_trait! {
         /// ```
         #[cfg(feature = "unstable")]
         #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
-        fn delay(self, dur: Duration) -> impl Future<Output = Self::Output> [DelayFuture<Self>]
+        fn delay(self, dur: Duration) -> [DelayFuture<Self>]
         where
             Self: Sized,
         {
@@ -70,8 +70,7 @@ extension_trait! {
         #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
         fn flatten(
             self,
-        ) -> impl Future<Output = <Self::Output as IntoFuture>::Output>
-            [FlattenFuture<Self, <Self::Output as IntoFuture>::Future>]
+        ) -> [FlattenFuture<Self, <Self::Output as IntoFuture>::Future>]
         where
             Self: Sized,
             <Self as Future>::Output: IntoFuture,
@@ -113,7 +112,7 @@ extension_trait! {
         fn race<F>(
             self,
             other: F,
-        ) -> impl Future<Output = <Self as std::future::Future>::Output> [Race<Self, F>]
+        ) -> [Race<Self, F>]
         where
             Self: std::future::Future + Sized,
             F: std::future::Future<Output = <Self as std::future::Future>::Output>,
@@ -159,7 +158,7 @@ extension_trait! {
         fn try_race<F, T, E>(
             self,
             other: F
-        ) -> impl Future<Output = <Self as std::future::Future>::Output> [TryRace<Self, F>]
+        ) -> [TryRace<Self, F>]
         where
             Self: std::future::Future<Output = Result<T, E>> + Sized,
             F: std::future::Future<Output = <Self as std::future::Future>::Output>,
@@ -196,7 +195,7 @@ extension_trait! {
         fn join<F>(
             self,
             other: F
-        ) -> impl Future<Output = (<Self as std::future::Future>::Output, <F as std::future::Future>::Output)> [Join<Self, F>]
+        ) -> [Join<Self, F>]
         where
             Self: std::future::Future + Sized,
             F: std::future::Future,
@@ -243,7 +242,7 @@ extension_trait! {
         fn try_join<F, A, B, E>(
             self,
             other: F
-        ) -> impl Future<Output = Result<(A, B), E>> [TryJoin<Self, F>]
+        ) -> [TryJoin<Self, F>]
         where
             Self: std::future::Future<Output = Result<A, E>> + Sized,
             F: std::future::Future<Output = Result<B, E>>,
@@ -279,7 +278,7 @@ extension_trait! {
         "#]
         #[cfg(any(all(feature = "default", feature = "unstable"), feature = "docs"))]
         #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
-        fn timeout(self, dur: Duration) -> impl Future<Output = Self::Output> [TimeoutFuture<Self>]
+        fn timeout(self, dur: Duration) -> [TimeoutFuture<Self>]
             where Self: Sized
         {
             TimeoutFuture::new(self, dur)
diff --git a/src/io/buf_read/mod.rs b/src/io/buf_read/mod.rs
index d42cbd8a3..2b1ee86b5 100644
--- a/src/io/buf_read/mod.rs
+++ b/src/io/buf_read/mod.rs
@@ -78,7 +78,7 @@ extension_trait! {
             &'a mut self,
             byte: u8,
             buf: &'a mut Vec<u8>,
-        ) -> impl Future<Output = usize> [ReadUntilFuture<'a, Self>]
+        ) -> [ReadUntilFuture<'a, Self>]
         where
             Self: Unpin,
         {
@@ -131,7 +131,7 @@ extension_trait! {
         fn read_line<'a>(
             &'a mut self,
             buf: &'a mut String,
-        ) -> impl Future<Output = io::Result<usize>> [ReadLineFuture<'a, Self>]
+        ) -> [ReadLineFuture<'a, Self>]
         where
             Self: Unpin,
         {
diff --git a/src/io/read/mod.rs b/src/io/read/mod.rs
index 12c7960e7..601bb7f1f 100644
--- a/src/io/read/mod.rs
+++ b/src/io/read/mod.rs
@@ -64,7 +64,7 @@ extension_trait! {
         fn read<'a>(
             &'a mut self,
             buf: &'a mut [u8],
-        ) -> impl Future<Output = io::Result<usize>> [ReadFuture<'a, Self>]
+        ) -> [ReadFuture<'a, Self>]
         where
             Self: Unpin
         {
@@ -86,7 +86,7 @@ extension_trait! {
         fn read_vectored<'a>(
             &'a mut self,
             bufs: &'a mut [IoSliceMut<'a>],
-        ) -> impl Future<Output = io::Result<usize>> [ReadVectoredFuture<'a, Self>]
+        ) -> [ReadVectoredFuture<'a, Self>]
         where
             Self: Unpin,
         {
@@ -123,7 +123,7 @@ extension_trait! {
         fn read_to_end<'a>(
             &'a mut self,
             buf: &'a mut Vec<u8>,
-        ) -> impl Future<Output = io::Result<usize>> [ReadToEndFuture<'a, Self>]
+        ) -> [ReadToEndFuture<'a, Self>]
         where
             Self: Unpin,
         {
@@ -162,7 +162,7 @@ extension_trait! {
         fn read_to_string<'a>(
             &'a mut self,
             buf: &'a mut String,
-        ) -> impl Future<Output = io::Result<usize>> [ReadToStringFuture<'a, Self>]
+        ) -> [ReadToStringFuture<'a, Self>]
         where
             Self: Unpin,
         {
@@ -217,7 +217,7 @@ extension_trait! {
         fn read_exact<'a>(
             &'a mut self,
             buf: &'a mut [u8],
-        ) -> impl Future<Output = io::Result<()>> [ReadExactFuture<'a, Self>]
+        ) -> [ReadExactFuture<'a, Self>]
         where
             Self: Unpin,
         {
diff --git a/src/io/seek/mod.rs b/src/io/seek/mod.rs
index c5ca6c611..297232232 100644
--- a/src/io/seek/mod.rs
+++ b/src/io/seek/mod.rs
@@ -40,7 +40,7 @@ extension_trait! {
         fn seek(
             &mut self,
             pos: SeekFrom,
-        ) -> impl Future<Output = io::Result<u64>> [SeekFuture<'_, Self>]
+        ) -> [SeekFuture<'_, Self>]
         where
             Self: Unpin,
         {
diff --git a/src/io/write/mod.rs b/src/io/write/mod.rs
index d000ad7cd..c8befae3d 100644
--- a/src/io/write/mod.rs
+++ b/src/io/write/mod.rs
@@ -49,7 +49,7 @@ extension_trait! {
         fn write<'a>(
             &'a mut self,
             buf: &'a [u8],
-        ) -> impl Future<Output = io::Result<usize>> [WriteFuture<'a, Self>]
+        ) -> [WriteFuture<'a, Self>]
         where
             Self: Unpin,
         {
@@ -75,7 +75,7 @@ extension_trait! {
             # Ok(()) }) }
             ```
         "#]
-        fn flush(&mut self) -> impl Future<Output = io::Result<()>> [FlushFuture<'_, Self>]
+        fn flush(&mut self) -> [FlushFuture<'_, Self>]
         where
             Self: Unpin,
         {
@@ -97,7 +97,7 @@ extension_trait! {
         fn write_vectored<'a>(
             &'a mut self,
             bufs: &'a [IoSlice<'a>],
-        ) -> impl Future<Output = io::Result<usize>> [WriteVectoredFuture<'a, Self>]
+        ) -> [WriteVectoredFuture<'a, Self>]
         where
             Self: Unpin,
         {
@@ -133,7 +133,7 @@ extension_trait! {
         fn write_all<'a>(
             &'a mut self,
             buf: &'a [u8],
-        ) -> impl Future<Output = io::Result<()>> [WriteAllFuture<'a, Self>]
+        ) -> [WriteAllFuture<'a, Self>]
         where
             Self: Unpin,
         {
@@ -170,7 +170,7 @@ extension_trait! {
         fn write_fmt<'a>(
             &'a mut self,
             fmt: std::fmt::Arguments<'_>,
-        ) -> impl Future<Output = io::Result<()>> [WriteFmtFuture<'a, Self>]
+        ) -> [WriteFmtFuture<'a, Self>]
         where
             Self: Unpin,
         {
diff --git a/src/stream/stream/mod.rs b/src/stream/stream/mod.rs
index a316893d6..d71dc6090 100644
--- a/src/stream/stream/mod.rs
+++ b/src/stream/stream/mod.rs
@@ -177,7 +177,7 @@ extension_trait! {
             # }) }
             ```
         "#]
-        fn next(&mut self) -> impl Future<Output = Option<Self::Item>> [NextFuture<'_, Self>]
+        fn next(&mut self) -> [NextFuture<'_, Self>]
         where
             Self: Unpin,
         {
@@ -629,7 +629,7 @@ extension_trait! {
         "#]
         fn last(
             self,
-        ) -> impl Future<Output = Option<Self::Item>> [LastFuture<Self, Self::Item>]
+        ) -> [LastFuture<Self, Self::Item>]
         where
             Self: Sized,
         {
@@ -839,7 +839,7 @@ extension_trait! {
         fn min_by_key<B, F>(
             self,
             key_by: F,
-        ) -> impl Future<Output = Option<Self::Item>> [MinByKeyFuture<Self, Self::Item, F>]
+        ) -> [MinByKeyFuture<Self, Self::Item, F>]
         where
             Self: Sized,
             B: Ord,
@@ -875,7 +875,7 @@ extension_trait! {
         fn max_by_key<B, F>(
             self,
             key_by: F,
-        ) -> impl Future<Output = Option<Self::Item>> [MaxByKeyFuture<Self, Self::Item, F>]
+        ) -> [MaxByKeyFuture<Self, Self::Item, F>]
         where
             Self: Sized,
             B: Ord,
@@ -914,7 +914,7 @@ extension_trait! {
         fn min_by<F>(
             self,
             compare: F,
-        ) -> impl Future<Output = Option<Self::Item>> [MinByFuture<Self, F, Self::Item>]
+        ) -> [MinByFuture<Self, F, Self::Item>]
         where
             Self: Sized,
             F: FnMut(&Self::Item, &Self::Item) -> Ordering,
@@ -947,7 +947,7 @@ extension_trait! {
         "#]
         fn max(
             self,
-        ) -> impl Future<Output = Option<Self::Item>> [MaxFuture<Self, Self::Item>]
+        ) -> [MaxFuture<Self, Self::Item>]
         where
             Self: Sized,
             Self::Item: Ord,
@@ -980,7 +980,7 @@ extension_trait! {
         "#]
         fn min(
             self,
-        ) -> impl Future<Output = Option<Self::Item>> [MinFuture<Self, Self::Item>]
+        ) -> [MinFuture<Self, Self::Item>]
         where
             Self: Sized,
             Self::Item: Ord,
@@ -1018,7 +1018,7 @@ extension_trait! {
         fn max_by<F>(
             self,
             compare: F,
-        ) -> impl Future<Output = Option<Self::Item>> [MaxByFuture<Self, F, Self::Item>]
+        ) -> [MaxByFuture<Self, F, Self::Item>]
         where
             Self: Sized,
             F: FnMut(&Self::Item, &Self::Item) -> Ordering,
@@ -1082,7 +1082,7 @@ extension_trait! {
         fn nth(
             &mut self,
             n: usize,
-        ) -> impl Future<Output = Option<Self::Item>> [NthFuture<'_, Self>]
+        ) -> [NthFuture<'_, Self>]
         where
             Self: Unpin + Sized,
         {
@@ -1138,7 +1138,7 @@ extension_trait! {
         fn all<F>(
             &mut self,
             f: F,
-        ) -> impl Future<Output = bool> [AllFuture<'_, Self, F, Self::Item>]
+        ) -> [AllFuture<'_, Self, F, Self::Item>]
         where
             Self: Unpin + Sized,
             F: FnMut(Self::Item) -> bool,
@@ -1187,7 +1187,7 @@ extension_trait! {
         fn find<P>(
             &mut self,
             p: P,
-        ) -> impl Future<Output = Option<Self::Item>> [FindFuture<'_, Self, P>]
+        ) -> [FindFuture<'_, Self, P>]
         where
             Self: Unpin + Sized,
             P: FnMut(&Self::Item) -> bool,
@@ -1215,7 +1215,7 @@ extension_trait! {
         fn find_map<F, B>(
             &mut self,
             f: F,
-        ) -> impl Future<Output = Option<B>> [FindMapFuture<'_, Self, F>]
+        ) -> [FindMapFuture<'_, Self, F>]
         where
             Self: Unpin + Sized,
             F: FnMut(Self::Item) -> Option<B>,
@@ -1249,7 +1249,7 @@ extension_trait! {
             self,
             init: B,
             f: F,
-        ) -> impl Future<Output = B> [FoldFuture<Self, F, B>]
+        ) -> [FoldFuture<Self, F, B>]
         where
             Self: Sized,
             F: FnMut(B, Self::Item) -> B,
@@ -1286,7 +1286,7 @@ extension_trait! {
         fn partition<B, F>(
             self,
             f: F,
-        ) -> impl Future<Output = (B, B)> [PartitionFuture<Self, F, B>]
+        ) -> [PartitionFuture<Self, F, B>]
         where
             Self: Sized,
             F: FnMut(&Self::Item) -> bool,
@@ -1322,7 +1322,7 @@ extension_trait! {
         fn for_each<F>(
             self,
             f: F,
-        ) -> impl Future<Output = ()> [ForEachFuture<Self, F>]
+        ) -> [ForEachFuture<Self, F>]
         where
             Self: Sized,
             F: FnMut(Self::Item),
@@ -1378,7 +1378,7 @@ extension_trait! {
         fn any<F>(
             &mut self,
             f: F,
-        ) -> impl Future<Output = bool> [AnyFuture<'_, Self, F, Self::Item>]
+        ) -> [AnyFuture<'_, Self, F, Self::Item>]
         where
             Self: Unpin + Sized,
             F: FnMut(Self::Item) -> bool,
@@ -1614,7 +1614,7 @@ extension_trait! {
             &mut self,
             init: T,
             f: F,
-        ) -> impl Future<Output = Result<T, E>> [TryFoldFuture<'_, Self, F, T>]
+        ) -> [TryFoldFuture<'_, Self, F, T>]
         where
             Self: Unpin + Sized,
             F: FnMut(B, Self::Item) -> Result<T, E>,
@@ -1659,7 +1659,7 @@ extension_trait! {
         fn try_for_each<F, E>(
             &mut self,
             f: F,
-        ) -> impl Future<Output = E> [TryForEachFuture<'_, Self, F>]
+        ) -> [TryForEachFuture<'_, Self, F>]
         where
             Self: Unpin + Sized,
             F: FnMut(Self::Item) -> Result<(), E>,
@@ -1741,7 +1741,7 @@ extension_trait! {
         "#]
         #[cfg(feature = "unstable")]
         #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
-        fn unzip<A, B, FromA, FromB>(self) -> impl Future<Output = (FromA, FromB)> [UnzipFuture<Self, FromA, FromB>]
+        fn unzip<A, B, FromA, FromB>(self) -> [UnzipFuture<Self, FromA, FromB>]
         where
         FromA: Default + Extend<A>,
         FromB: Default + Extend<B>,
@@ -1805,7 +1805,7 @@ extension_trait! {
         #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
         fn collect<'a, B>(
             self,
-        ) -> impl Future<Output = B> [Pin<Box<dyn Future<Output = B> + 'a + Send>>]
+        ) -> [Pin<Box<dyn Future<Output = B> + 'a + Send>>]
         where
             Self: Sized + 'a + Send,
             B: FromStream<Self::Item>,
@@ -1879,7 +1879,7 @@ extension_trait! {
         fn partial_cmp<S>(
            self,
            other: S
-        ) -> impl Future<Output = Option<Ordering>>  [PartialCmpFuture<Self, S>]
+        ) -> [PartialCmpFuture<Self, S>]
         where
             Self: Sized + Stream,
             S: Stream,
@@ -1919,7 +1919,7 @@ extension_trait! {
         fn position<P>(
            &mut self,
            predicate: P,
-        ) -> impl Future<Output = Option<usize>> [PositionFuture<'_, Self, P>]
+        ) -> [PositionFuture<'_, Self, P>]
         where
             Self: Unpin + Sized,
             P: FnMut(Self::Item) -> bool,
@@ -1957,7 +1957,7 @@ extension_trait! {
         fn cmp<S>(
            self,
            other: S
-        ) -> impl Future<Output = Ordering> [CmpFuture<Self, S>]
+        ) -> [CmpFuture<Self, S>]
         where
             Self: Sized + Stream,
             S: Stream,
@@ -1988,7 +1988,7 @@ extension_trait! {
         "#]
         #[cfg(feature = "unstable")]
         #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
-        fn count(self) -> impl Future<Output = usize> [CountFuture<Self>]
+        fn count(self) -> [CountFuture<Self>]
         where
             Self: Sized,
         {
@@ -2023,7 +2023,7 @@ extension_trait! {
         fn ne<S>(
            self,
            other: S
-        ) -> impl Future<Output = bool> [NeFuture<Self, S>]
+        ) -> [NeFuture<Self, S>]
         where
             Self: Sized,
             S: Sized + Stream,
@@ -2060,7 +2060,7 @@ extension_trait! {
         fn ge<S>(
            self,
            other: S
-        ) -> impl Future<Output = bool> [GeFuture<Self, S>]
+        ) -> [GeFuture<Self, S>]
         where
             Self: Sized + Stream,
             S: Stream,
@@ -2097,7 +2097,7 @@ extension_trait! {
         fn eq<S>(
            self,
            other: S
-        ) -> impl Future<Output = bool> [EqFuture<Self, S>]
+        ) -> [EqFuture<Self, S>]
         where
             Self: Sized + Stream,
             S: Sized + Stream,
@@ -2134,7 +2134,7 @@ extension_trait! {
         fn gt<S>(
            self,
            other: S
-        ) -> impl Future<Output = bool> [GtFuture<Self, S>]
+        ) -> [GtFuture<Self, S>]
         where
             Self: Sized + Stream,
             S: Stream,
@@ -2171,7 +2171,7 @@ extension_trait! {
         fn le<S>(
            self,
            other: S
-        ) -> impl Future<Output = bool> [LeFuture<Self, S>]
+        ) -> [LeFuture<Self, S>]
         where
             Self: Sized + Stream,
             S: Stream,
@@ -2208,7 +2208,7 @@ extension_trait! {
         fn lt<S>(
            self,
            other: S
-        ) -> impl Future<Output = bool> [LtFuture<Self, S>]
+        ) -> [LtFuture<Self, S>]
         where
             Self: Sized + Stream,
             S: Stream,
@@ -2252,7 +2252,7 @@ extension_trait! {
         #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
         fn sum<'a, S>(
             self,
-        ) -> impl Future<Output = S> [Pin<Box<dyn Future<Output = S> + 'a>>]
+        ) -> [Pin<Box<dyn Future<Output = S> + 'a>>]
         where
             Self: Sized + Stream<Item = S> + 'a,
             S: Sum<Self::Item>,
@@ -2298,7 +2298,7 @@ extension_trait! {
         #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
         fn product<'a, P>(
             self,
-        ) -> impl Future<Output = P> [Pin<Box<dyn Future<Output = P> + 'a>>]
+        ) -> [Pin<Box<dyn Future<Output = P> + 'a>>]
         where
             Self: Sized + Stream<Item = P> + 'a,
             P: Product,
diff --git a/src/utils.rs b/src/utils.rs
index 42286ad11..1f3b7fc82 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -271,7 +271,7 @@ macro_rules! extension_trait {
     };
 
     // Parse the return type in an extension method.
-    (@ext [-> impl Future<Output = $out:ty> [$f:ty] $($tail:tt)*] -> [$($accum:tt)*]) => {
+    (@ext [-> [$f:ty] $($tail:tt)*] -> [$($accum:tt)*]) => {
         extension_trait!(@ext [$($tail)*] -> [$($accum)* -> $f]);
     };