diff --git a/core/Cargo.toml b/core/Cargo.toml
index 2bf1ae35cb1..77fecdc486c 100644
--- a/core/Cargo.toml
+++ b/core/Cargo.toml
@@ -22,7 +22,7 @@ log = "0.4"
 multiaddr = { package = "parity-multiaddr", version = "0.5.0", path = "../misc/multiaddr" }
 multihash = { package = "parity-multihash", version = "0.1.0", path = "../misc/multihash" }
 multistream-select = { version = "0.5.0", path = "../misc/multistream-select" }
-futures-preview = { version = "= 0.3.0-alpha.18", features = ["compat", "io-compat"] }
+futures-preview = { version = "0.3.0-alpha.18", features = ["compat", "io-compat"] }
 parking_lot = "0.8"
 protobuf = "2.8"
 quick-error = "1.2"
diff --git a/core/src/either.rs b/core/src/either.rs
index b81691a3143..f1b69e41bc6 100644
--- a/core/src/either.rs
+++ b/core/src/either.rs
@@ -19,7 +19,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 use crate::{muxing::StreamMuxer, ProtocolName, transport::ListenerEvent};
-use futures::{prelude::*, io::Initializer};
+use futures::prelude::*;
 use std::{fmt, io::{Error as IoError, Read, Write}, pin::Pin, task::Context, task::Poll};
 
 #[derive(Debug, Copy, Clone)]
@@ -67,13 +67,6 @@ where
     A: AsyncRead + Unpin,
     B: AsyncRead + Unpin,
 {
-    unsafe fn initializer(&self) -> Initializer {
-        match self {
-            EitherOutput::First(a) => a.initializer(),
-            EitherOutput::Second(b) => b.initializer(),
-        }
-    }
-
     fn poll_read(mut self: Pin<&mut Self>, cx: &mut Context, buf: &mut [u8]) -> Poll<Result<usize, IoError>> {
         match &mut *self {
             EitherOutput::First(a) => AsyncRead::poll_read(Pin::new(a), cx, buf),
@@ -249,13 +242,6 @@ where
         }
     }
 
-    unsafe fn initializer(&self) -> Initializer {
-        match self {
-            EitherOutput::First(ref inner) => inner.initializer(),
-            EitherOutput::Second(ref inner) => inner.initializer(),
-        }
-    }
-
     fn read_substream(&self, cx: &mut Context, sub: &mut Self::Substream, buf: &mut [u8]) -> Poll<Result<usize, Self::Error>> {
         match (self, sub) {
             (EitherOutput::First(ref inner), EitherOutput::First(ref mut sub)) => {
diff --git a/core/src/muxing.rs b/core/src/muxing.rs
index 0ed2068a088..c6a8aa6862c 100644
--- a/core/src/muxing.rs
+++ b/core/src/muxing.rs
@@ -52,7 +52,7 @@
 //! implementation of `StreamMuxer` to control everything that happens on the wire.
 
 use fnv::FnvHashMap;
-use futures::{future, prelude::*, io::Initializer, task::Context, task::Poll};
+use futures::{future, prelude::*, task::Context, task::Poll};
 use parking_lot::Mutex;
 use std::{io, ops::Deref, fmt, pin::Pin, sync::atomic::{AtomicUsize, Ordering}};
 
@@ -130,11 +130,6 @@ pub trait StreamMuxer {
     fn read_substream(&self, cx: &mut Context, s: &mut Self::Substream, buf: &mut [u8])
         -> Poll<Result<usize, Self::Error>>;
 
-    /// Mimics the `initializer` method of the `AsyncRead` trait.
-    unsafe fn initializer(&self) -> Initializer {
-        Initializer::zeroing()
-    }
-
     /// Write data to a substream. The behaviour is the same as `futures::AsyncWrite::poll_write`.
     ///
     /// If `Pending` is returned, then the current task will be notified once the substream
@@ -381,10 +376,6 @@ where
     P: Deref,
     P::Target: StreamMuxer,
 {
-    unsafe fn initializer(&self) -> Initializer {
-        self.muxer.initializer()
-    }
-
     fn poll_read(mut self: Pin<&mut Self>, cx: &mut Context, buf: &mut [u8]) -> Poll<Result<usize, io::Error>> {
         // We use a `this` because the compiler isn't smart enough to allow mutably borrowing
         // multiple different fields from the `Pin` at the same time.
@@ -511,10 +502,6 @@ impl StreamMuxer for StreamMuxerBox {
         self.inner.destroy_outbound(substream)
     }
 
-    unsafe fn initializer(&self) -> Initializer {
-        self.inner.initializer()
-    }
-
     #[inline]
     fn read_substream(&self, cx: &mut Context, s: &mut Self::Substream, buf: &mut [u8]) -> Poll<Result<usize, Self::Error>> {
         self.inner.read_substream(cx, s, buf)
@@ -616,10 +603,6 @@ where
         self.inner.destroy_outbound(list.remove(&substream).unwrap())
     }
 
-    unsafe fn initializer(&self) -> Initializer {
-        self.inner.initializer()
-    }
-
     #[inline]
     fn read_substream(&self, cx: &mut Context, s: &mut Self::Substream, buf: &mut [u8]) -> Poll<Result<usize, Self::Error>> {
         let mut list = self.substreams.lock();
diff --git a/core/src/muxing/singleton.rs b/core/src/muxing/singleton.rs
index f85e22fd69f..c2b56d0c131 100644
--- a/core/src/muxing/singleton.rs
+++ b/core/src/muxing/singleton.rs
@@ -19,7 +19,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 use crate::{Endpoint, muxing::StreamMuxer};
-use futures::{prelude::*, io::Initializer};
+use futures::prelude::*;
 use parking_lot::Mutex;
 use std::{io, pin::Pin, sync::atomic::{AtomicBool, Ordering}, task::Context, task::Poll};
 
@@ -100,10 +100,6 @@ where
     fn destroy_outbound(&self, _: Self::OutboundSubstream) {
     }
 
-    unsafe fn initializer(&self) -> Initializer {
-        self.inner.lock().initializer()
-    }
-
     fn read_substream(&self, cx: &mut Context, _: &mut Self::Substream, buf: &mut [u8]) -> Poll<Result<usize, io::Error>> {
         let res = AsyncRead::poll_read(Pin::new(&mut *self.inner.lock()), cx, buf);
         if let Poll::Ready(Ok(_)) = res {
diff --git a/misc/rw-stream-sink/Cargo.toml b/misc/rw-stream-sink/Cargo.toml
index a8c2d1008b1..0ed7701bda6 100644
--- a/misc/rw-stream-sink/Cargo.toml
+++ b/misc/rw-stream-sink/Cargo.toml
@@ -10,4 +10,4 @@ keywords = ["networking"]
 categories = ["network-programming", "asynchronous"]
 
 [dependencies]
-futures-preview = "= 0.3.0-alpha.18"
+futures-preview = "0.3.0-alpha.18"
diff --git a/misc/rw-stream-sink/src/lib.rs b/misc/rw-stream-sink/src/lib.rs
index f64510410b7..c4e6ec63eab 100644
--- a/misc/rw-stream-sink/src/lib.rs
+++ b/misc/rw-stream-sink/src/lib.rs
@@ -27,7 +27,7 @@
 //! > **Note**: Although this crate is hosted in the libp2p repo, it is purely a utility crate and
 //! >           not at all specific to libp2p.
 
-use futures::{prelude::*, io::Initializer};
+use futures::prelude::*;
 use std::{cmp, io, pin::Pin, task::Context, task::Poll};
 
 /// Wraps around a `Stream + Sink` whose items are buffers. Implements `AsyncRead` and `AsyncWrite`.
@@ -74,10 +74,6 @@ where
         for _ in 0..to_copy { current_item.remove(0); }
         Poll::Ready(Ok(to_copy))
     }
-
-    unsafe fn initializer(&self) -> Initializer {
-        Initializer::nop()
-    }
 }
 
 impl<S> AsyncWrite for RwStreamSink<S>
diff --git a/muxers/mplex/src/lib.rs b/muxers/mplex/src/lib.rs
index e3a9ff06f6e..0c97cbe2047 100644
--- a/muxers/mplex/src/lib.rs
+++ b/muxers/mplex/src/lib.rs
@@ -33,7 +33,7 @@ use libp2p_core::{
 use log::{debug, trace};
 use parking_lot::Mutex;
 use fnv::FnvHashSet;
-use futures::{prelude::*, future, io::Initializer, ready, stream::Fuse};
+use futures::{prelude::*, future, ready, stream::Fuse};
 use futures::task::{ArcWake, waker_ref};
 use futures_codec::Framed;
 
@@ -470,10 +470,6 @@ where C: AsyncRead + AsyncWrite + Unpin
         // Nothing to do.
     }
 
-    unsafe fn initializer(&self) -> Initializer {
-        Initializer::nop()
-    }
-
     fn read_substream(&self, cx: &mut Context, substream: &mut Self::Substream, buf: &mut [u8]) -> Poll<Result<usize, IoError>> {
         loop {
             // First, transfer from `current_data`.
diff --git a/muxers/yamux/src/lib.rs b/muxers/yamux/src/lib.rs
index dd062a6daef..c19f12f0176 100644
--- a/muxers/yamux/src/lib.rs
+++ b/muxers/yamux/src/lib.rs
@@ -80,10 +80,6 @@ where
     fn destroy_outbound(&self, _: Self::OutboundSubstream) {
     }
 
-    unsafe fn prepare_uninitialized_buffer(&self, _: &mut [u8]) -> bool {
-        false
-    }
-
     fn read_substream(&self, sub: &mut Self::Substream, buf: &mut [u8]) -> Poll<usize, IoError> {
         let result = sub.poll_read(buf);
         if let Ok(Async::Ready(_)) = result {
diff --git a/protocols/deflate/src/lib.rs b/protocols/deflate/src/lib.rs
index 74f33c691a6..0a2719683a4 100644
--- a/protocols/deflate/src/lib.rs
+++ b/protocols/deflate/src/lib.rs
@@ -135,7 +135,6 @@ impl<S> AsyncRead for DeflateOutput<S>
                 unsafe {
                     this.read_interm.reserve(256);
                     this.read_interm.set_len(this.read_interm.capacity());
-                    this.inner.initializer().initialize(&mut this.read_interm);
                 }
 
                 match AsyncRead::poll_read(Pin::new(&mut this.inner), cx, &mut this.read_interm) {
@@ -172,10 +171,6 @@ impl<S> AsyncRead for DeflateOutput<S>
             }
         }
     }
-
-    unsafe fn initializer(&self) -> futures::io::Initializer {
-        futures::io::Initializer::nop()
-    }
 }
 
 impl<S> AsyncWrite for DeflateOutput<S>
diff --git a/protocols/noise/src/io.rs b/protocols/noise/src/io.rs
index 03964042c58..c1b6616cb55 100644
--- a/protocols/noise/src/io.rs
+++ b/protocols/noise/src/io.rs
@@ -252,10 +252,6 @@ impl<T: AsyncRead + Unpin> AsyncRead for NoiseOutput<T> {
             }
         }
     }
-
-    unsafe fn initializer(&self) -> futures::io::Initializer {
-        futures::io::Initializer::nop()
-    }
 }
 
 impl<T: AsyncWrite + Unpin> AsyncWrite for NoiseOutput<T> {
diff --git a/protocols/secio/src/lib.rs b/protocols/secio/src/lib.rs
index b9d43204702..9a0a103ab94 100644
--- a/protocols/secio/src/lib.rs
+++ b/protocols/secio/src/lib.rs
@@ -58,7 +58,7 @@
 pub use self::error::SecioError;
 
 use futures::stream::MapErr as StreamMapErr;
-use futures::{prelude::*, io::Initializer};
+use futures::prelude::*;
 use libp2p_core::{PeerId, PublicKey, identity, upgrade::{UpgradeInfo, InboundUpgrade, OutboundUpgrade, Negotiated}};
 use log::debug;
 use rw_stream_sink::RwStreamSink;
@@ -199,10 +199,6 @@ impl<S: AsyncRead + AsyncWrite + Unpin> AsyncRead for SecioOutput<S> {
     {
         AsyncRead::poll_read(Pin::new(&mut self.stream), cx, buf)
     }
-
-    unsafe fn initializer(&self) -> Initializer {
-        self.stream.initializer()
-    }
 }
 
 impl<S: AsyncRead + AsyncWrite + Unpin> AsyncWrite for SecioOutput<S> {
diff --git a/transports/tcp/src/lib.rs b/transports/tcp/src/lib.rs
index ea90a5f865a..a9e7740e44d 100644
--- a/transports/tcp/src/lib.rs
+++ b/transports/tcp/src/lib.rs
@@ -39,7 +39,6 @@
 use async_std::net::TcpStream;
 use futures::{
     future::{self, Ready},
-    io::Initializer,
     prelude::*,
 };
 use futures_timer::Delay;
@@ -420,10 +419,6 @@ impl AsyncRead for TcpTransStream {
     fn poll_read(mut self: Pin<&mut Self>, cx: &mut Context, buf: &mut [u8]) -> Poll<Result<usize, io::Error>> {
         AsyncRead::poll_read(Pin::new(&mut self.inner), cx, buf)
     }
-
-    unsafe fn initializer(&self) -> Initializer {
-        self.inner.initializer()
-    }
 }
 
 impl AsyncWrite for TcpTransStream {
diff --git a/transports/wasm-ext/src/lib.rs b/transports/wasm-ext/src/lib.rs
index ffed6e59cc1..64026eef46c 100644
--- a/transports/wasm-ext/src/lib.rs
+++ b/transports/wasm-ext/src/lib.rs
@@ -32,7 +32,7 @@
 //! module.
 //!
 
-use futures::{prelude::*, future::Ready, io::Initializer};
+use futures::{prelude::*, future::Ready};
 use libp2p_core::{transport::ListenerEvent, transport::TransportError, Multiaddr, Transport};
 use parity_send_wrapper::SendWrapper;
 use std::{collections::VecDeque, error, fmt, io, mem, pin::Pin, task::Context, task::Poll};
@@ -356,10 +356,6 @@ impl fmt::Debug for Connection {
 }
 
 impl AsyncRead for Connection {
-    unsafe fn initializer(&self) -> Initializer {
-        Initializer::nop()
-    }
-
     fn poll_read(mut self: Pin<&mut Self>, cx: &mut Context, buf: &mut [u8]) -> Poll<Result<usize, io::Error>> {
         loop {
             match mem::replace(&mut self.read_state, ConnectionReadState::Finished) {
diff --git a/transports/websocket/Cargo.toml b/transports/websocket/Cargo.toml
index 30e7c8b589a..517a45bff23 100644
--- a/transports/websocket/Cargo.toml
+++ b/transports/websocket/Cargo.toml
@@ -12,7 +12,7 @@ categories = ["network-programming", "asynchronous"]
 [dependencies]
 bytes = "0.4.12"
 either = "1.5.3"
-futures-preview = "= 0.3.0-alpha.18"
+futures-preview = "0.3.0-alpha.18"
 #futures-rustls = "0.12.0-alpha"        # TODO: https://github.com/quininer/tokio-rustls/issues/51
 libp2p-core = { version = "0.12.0", path = "../../core" }
 log = "0.4.8"