diff --git a/.cirrus.yml b/.cirrus.yml
index c3d87611bd..132a048d59 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -39,7 +39,7 @@ task:
     image: freebsd-12-2-release-amd64
   setup_script:
     - fetch https://sh.rustup.rs -o rustup.sh
-    - sh rustup.sh -y --profile=minimal --default-toolchain $TOOLCHAIN
+    - sh rustup.sh -y --profile=minimal --default-toolchain 1.41.0
     - . $HOME/.cargo/env
     - rustup target add i686-unknown-freebsd
     - rustup component add --toolchain $TOOLCHAIN clippy
@@ -57,11 +57,32 @@ task:
     - name: OSX x86_64
       env:
         TARGET: x86_64-apple-darwin
+<<<<<<< HEAD
+=======
+    - name: OSX i686
+      env:
+        TARGET: i686-apple-darwin
+        DISABLE_TESTS: 1
+    - name: iOS
+      env:
+        # To save VM startup time, test all iOS targets in a single task.
+        # The startup and scheduling time was very significant for Travis, but
+        # not known for Cirrus.
+        TARGET: "aarch64-apple-ios;armv7-apple-ios;armv7s-apple-ios;i386-apple-ios;x86_64-apple-ios"
+        DISABLE_TESTS: 1
+>>>>>>> parent of 5ed5bb6 (Merge pull request #1492 from asomers/bitflags_1.3.1)
   osx_instance:
     image: catalina-xcode
   setup_script:
     - curl --proto '=https' --tlsv1.2 -sSf -o rustup.sh https://sh.rustup.rs
+<<<<<<< HEAD
     - sh rustup.sh -y --profile=minimal --default-toolchain $TOOLCHAIN
+=======
+    - sh rustup.sh -y --profile=minimal --default-toolchain 1.41.0
+    - . $HOME/.cargo/env
+    - bash ci/install.sh
+  script:
+>>>>>>> parent of 5ed5bb6 (Merge pull request #1492 from asomers/bitflags_1.3.1)
     - . $HOME/.cargo/env
     - rustup component add --toolchain $TOOLCHAIN clippy
   << : *TEST
@@ -113,7 +134,11 @@ task:
   setup_script:
     - mkdir /tmp/home
     - curl --proto '=https' --tlsv1.2 -sSf -o rustup.sh https://sh.rustup.rs
+<<<<<<< HEAD
     - sh rustup.sh -y --profile=minimal --default-toolchain $TOOLCHAIN
+=======
+    - sh rustup.sh -y --profile=minimal --default-toolchain 1.41.0
+>>>>>>> parent of 5ed5bb6 (Merge pull request #1492 from asomers/bitflags_1.3.1)
     - . $HOME/.cargo/env
     - cargo install cross
   << : *TEST
@@ -139,11 +164,21 @@ task:
         image: rust:1.46
       env:
         TARGET: x86_64-unknown-linux-gnu
+<<<<<<< HEAD
+=======
+        TOOLCHAIN: 1.41.0
+>>>>>>> parent of 5ed5bb6 (Merge pull request #1492 from asomers/bitflags_1.3.1)
     - name: Linux x86_64 musl
       container:
         image: rust:1.46
       env:
         TARGET: x86_64-unknown-linux-musl
+<<<<<<< HEAD
+=======
+        TOOLCHAIN: 1.41.0
+  container:
+    image: rust:1.41
+>>>>>>> parent of 5ed5bb6 (Merge pull request #1492 from asomers/bitflags_1.3.1)
   setup_script:
     - rustup target add $TARGET
     - rustup component add clippy
@@ -221,11 +256,32 @@ task:
         TARGET: x86_64-unknown-netbsd
     - name: Redox x86_64
       env:
+<<<<<<< HEAD
         TARGET: x86_64-unknown-redox
         # Redox requires a nightly compiler.
         # If stuff breaks, change nightly to the date in the toolchain_*
         # directory at https://static.redox-os.org
         TOOLCHAIN: nightly-2020-08-04
+=======
+        TARGET: x86_64-fuchsia
+  container:
+    image: rust:1.41
+  setup_script:
+    - rustup target add $TARGET
+  script:
+    - cargo +$TOOLCHAIN check --target $TARGET
+    - cargo +$TOOLCHAIN check --target $TARGET --release
+    - cargo +$TOOLCHAIN check --all-targets --target $TARGET
+  before_cache_script: rm -rf $CARGO_HOME/registry/index
+
+# illumos toolchain isn't available via rustup until 1.50
+task:
+  name: illumos
+  env:
+    TARGET: x86_64-unknown-illumos
+  container:
+    image: rust:1.50
+>>>>>>> parent of 5ed5bb6 (Merge pull request #1492 from asomers/bitflags_1.3.1)
   setup_script:
     - rustup target add $TARGET
     - rustup toolchain install $TOOLCHAIN --profile minimal --target $TARGET
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 90c0075ecf..bb962ad678 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -69,6 +69,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Many more functions, mostly contructors, are now `const`.
   (#[1476](https://github.com/nix-rust/nix/pull/1476))
   (#[1492](https://github.com/nix-rust/nix/pull/1492))
+
 - `sys::event::KEvent::filter` now returns a `Result` instead of being
   infalliable.  The only cases where it will now return an error are cases
   where it previously would've had undefined behavior.
diff --git a/Cargo.toml b/Cargo.toml
index 298c16ebb8..bc5e337d55 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -26,7 +26,7 @@ targets = [
 
 [dependencies]
 libc = { version = "0.2.102", features = [ "extra_traits" ] }
-bitflags = "1.3.1"
+bitflags = "1.1"
 cfg-if = "1.0"
 
 [target.'cfg(not(target_os = "redox"))'.dependencies]
diff --git a/README.md b/README.md
index 296f83fb9a..616ba0a0c9 100644
--- a/README.md
+++ b/README.md
@@ -68,7 +68,11 @@ Tier 2:
   * aarch64-linux-android
   * arm-linux-androideabi
   * arm-unknown-linux-musleabi
+  * armv7-apple-ios
   * armv7-linux-androideabi
+  * armv7s-apple-ios
+  * i386-apple-ios
+  * i686-apple-darwin
   * i686-linux-android
   * powerpc-unknown-linux-gnu
   * s390x-unknown-linux-gnu
@@ -86,7 +90,7 @@ Tier 3:
 
 ## Usage
 
-`nix` requires Rust 1.46.0 or newer.
+`nix` requires Rust 1.41.0 or newer.
 
 To use `nix`, add this to your `Cargo.toml`:
 
diff --git a/src/errno.rs b/src/errno.rs
index 3da246e823..0b4a2ad0f3 100644
--- a/src/errno.rs
+++ b/src/errno.rs
@@ -94,7 +94,7 @@ impl Errno {
         desc(self)
     }
 
-    pub const fn from_i32(err: i32) -> Errno {
+    pub fn from_i32(err: i32) -> Errno {
         from_i32(err)
     }
 
@@ -930,7 +930,7 @@ mod consts {
         pub const ENOTSUP:     Errno = Errno::EOPNOTSUPP;
     }
 
-    pub const fn from_i32(e: i32) -> Errno {
+    pub fn from_i32(e: i32) -> Errno {
         use self::Errno::*;
 
         match e {
@@ -1209,7 +1209,7 @@ mod consts {
         pub const EDEADLOCK:   Errno = Errno::EDEADLK;
     }
 
-    pub const fn from_i32(e: i32) -> Errno {
+    pub fn from_i32(e: i32) -> Errno {
         use self::Errno::*;
 
         match e {
@@ -1457,7 +1457,7 @@ mod consts {
         pub const EOPNOTSUPP:  Errno = Errno::ENOTSUP;
     }
 
-    pub const fn from_i32(e: i32) -> Errno {
+    pub fn from_i32(e: i32) -> Errno {
         use self::Errno::*;
 
         match e {
@@ -1694,7 +1694,7 @@ mod consts {
         pub const EOPNOTSUPP:  Errno = Errno::ENOTSUP;
     }
 
-    pub const fn from_i32(e: i32) -> Errno {
+    pub fn from_i32(e: i32) -> Errno {
         use self::Errno::*;
 
         match e {
@@ -1918,7 +1918,7 @@ mod consts {
         pub const EWOULDBLOCK: Errno = Errno::EAGAIN;
     }
 
-    pub const fn from_i32(e: i32) -> Errno {
+    pub fn from_i32(e: i32) -> Errno {
         use self::Errno::*;
 
         match e {
@@ -2143,7 +2143,7 @@ mod consts {
         pub const EWOULDBLOCK: Errno = Errno::EAGAIN;
     }
 
-    pub const fn from_i32(e: i32) -> Errno {
+    pub fn from_i32(e: i32) -> Errno {
         use self::Errno::*;
 
         match e {
@@ -2352,7 +2352,7 @@ mod consts {
         pub const EWOULDBLOCK: Errno = Errno::EAGAIN;
     }
 
-    pub const fn from_i32(e: i32) -> Errno {
+    pub fn from_i32(e: i32) -> Errno {
         use self::Errno::*;
 
         match e {
@@ -2592,7 +2592,7 @@ mod consts {
         pub const EWOULDBLOCK: Errno = Errno::EAGAIN;
     }
 
-    pub const fn from_i32(e: i32) -> Errno {
+    pub fn from_i32(e: i32) -> Errno {
         use self::Errno::*;
 
         match e {
diff --git a/src/macros.rs b/src/macros.rs
index 3ccbfdd43b..927e7e7c76 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -113,9 +113,9 @@ macro_rules! libc_enum {
         $v enum $BitFlags {
             $($entries)*
         }
+        #[allow(unused_doc_comment)]
         impl ::std::convert::TryFrom<$repr> for $BitFlags {
             type Error = $crate::Error;
-            #[allow(unused_doc_comments)]
             fn try_from(x: $repr) -> $crate::Result<Self> {
                 match x {
                     $($try_froms)*
diff --git a/src/sys/signal.rs b/src/sys/signal.rs
index e8c79d3367..2630c9e2b9 100644
--- a/src/sys/signal.rs
+++ b/src/sys/signal.rs
@@ -167,7 +167,7 @@ impl Signal {
     /// This function is equivalent to `<Signal as AsRef<str>>::as_ref()`,
     /// with difference that returned string is `'static`
     /// and not bound to `self`'s lifetime.
-    pub const fn as_str(self) -> &'static str {
+    pub fn as_str(self) -> &'static str {
         match self {
             Signal::SIGHUP => "SIGHUP",
             Signal::SIGINT => "SIGINT",
diff --git a/src/sys/socket/addr.rs b/src/sys/socket/addr.rs
index b119642b3f..b84f83d5ec 100644
--- a/src/sys/socket/addr.rs
+++ b/src/sys/socket/addr.rs
@@ -237,7 +237,7 @@ impl AddressFamily {
     ///
     /// Currently only supports these address families: Unix, Inet (v4 & v6), Netlink, Link/Packet
     /// and System. Returns None for unsupported or unknown address families.
-    pub const fn from_i32(family: i32) -> Option<AddressFamily> {
+    pub fn from_i32(family: i32) -> Option<AddressFamily> {
         match family {
             libc::AF_UNIX => Some(AddressFamily::Unix),
             libc::AF_INET => Some(AddressFamily::Inet),
@@ -316,7 +316,7 @@ impl InetAddr {
         }
     }
     /// Gets the IP address associated with this socket address.
-    pub const fn ip(&self) -> IpAddr {
+    pub fn ip(&self) -> IpAddr {
         match *self {
             InetAddr::V4(ref sa) => IpAddr::V4(Ipv4Addr(sa.sin_addr)),
             InetAddr::V6(ref sa) => IpAddr::V6(Ipv6Addr(sa.sin6_addr)),
@@ -324,7 +324,7 @@ impl InetAddr {
     }
 
     /// Gets the port number associated with this socket address
-    pub const fn port(&self) -> u16 {
+    pub fn port(&self) -> u16 {
         match *self {
             InetAddr::V6(ref sa) => u16::from_be(sa.sin6_port),
             InetAddr::V4(ref sa) => u16::from_be(sa.sin_port),
@@ -396,7 +396,7 @@ impl IpAddr {
         }
     }
 
-    pub const fn to_std(&self) -> net::IpAddr {
+    pub fn to_std(&self) -> net::IpAddr {
         match *self {
             IpAddr::V4(ref ip) => net::IpAddr::V4(ip.to_std()),
             IpAddr::V6(ref ip) => net::IpAddr::V6(ip.to_std()),