diff --git a/src/bootstrap/bin/rustdoc.rs b/src/bootstrap/bin/rustdoc.rs
index a54e58665cceb..bb5a21e3e405f 100644
--- a/src/bootstrap/bin/rustdoc.rs
+++ b/src/bootstrap/bin/rustdoc.rs
@@ -37,6 +37,8 @@ fn main() {
     let mut dylib_path = bootstrap::util::dylib_path();
     dylib_path.insert(0, PathBuf::from(libdir.clone()));
 
+    //FIXME(misdreavus): once stdsimd uses cfg(rustdoc) instead of cfg(dox), remove the `--cfg dox`
+    //arguments here
     let mut cmd = Command::new(rustdoc);
     cmd.args(&args)
         .arg("--cfg")
diff --git a/src/doc/rustdoc/src/unstable-features.md b/src/doc/rustdoc/src/unstable-features.md
index a91c2cd71cde3..876a773b30ab0 100644
--- a/src/doc/rustdoc/src/unstable-features.md
+++ b/src/doc/rustdoc/src/unstable-features.md
@@ -106,27 +106,25 @@ The `#[doc(cfg(...))]` attribute has another effect: When Rustdoc renders docume
 item, it will be accompanied by a banner explaining that the item is only available on certain
 platforms.
 
-As mentioned earlier, getting the items to Rustdoc requires some extra preparation. The standard
-library adds a `--cfg dox` flag to every Rustdoc command, but the same thing can be accomplished by
-adding a feature to your Cargo.toml and adding `--feature dox` (or whatever you choose to name the
-feature) to your `cargo doc` calls.
+For Rustdoc to document an item, it needs to see it, regardless of what platform it's currently
+running on. To aid this, Rustdoc sets the flag `#[cfg(rustdoc)]` when running on your crate.
+Combining this with the target platform of a given item allows it to appear when building your crate
+normally on that platform, as well as when building documentation anywhere.
 
-Either way, once you create an environment for the documentation, you can start to augment your
-`#[cfg]` attributes to allow both the target platform *and* the documentation configuration to leave
-the item in. For example, `#[cfg(any(windows, feature = "dox"))]` will preserve the item either on
-Windows or during the documentation process. Then, adding a new attribute `#[doc(cfg(windows))]`
-will tell Rustdoc that the item is supposed to be used on Windows. For example:
+For example, `#[cfg(any(windows, rustdoc))]` will preserve the item either on Windows or during the
+documentation process. Then, adding a new attribute `#[doc(cfg(windows))]` will tell Rustdoc that
+the item is supposed to be used on Windows. For example:
 
 ```rust
 #![feature(doc_cfg)]
 
 /// Token struct that can only be used on Windows.
-#[cfg(any(windows, feature = "dox"))]
+#[cfg(any(windows, rustdoc))]
 #[doc(cfg(windows))]
 pub struct WindowsToken;
 
 /// Token struct that can only be used on Unix.
-#[cfg(any(unix, feature = "dox"))]
+#[cfg(any(unix, rustdoc))]
 #[doc(cfg(unix))]
 pub struct UnixToken;
 ```
diff --git a/src/doc/unstable-book/src/language-features/doc-cfg.md b/src/doc/unstable-book/src/language-features/doc-cfg.md
index ddc538e12144a..96c66a1515ed5 100644
--- a/src/doc/unstable-book/src/language-features/doc-cfg.md
+++ b/src/doc/unstable-book/src/language-features/doc-cfg.md
@@ -12,13 +12,17 @@ This attribute has two effects:
 
 2. The item's doc-tests will only run on the specific platform.
 
+In addition to allowing the use of the `#[doc(cfg)]` attribute, this feature enables the use of a
+special conditional compilation flag, `#[cfg(rustdoc)]`, set whenever building documentation on your
+crate.
+
 This feature was introduced as part of PR [#43348] to allow the platform-specific parts of the
 standard library be documented.
 
 ```rust
 #![feature(doc_cfg)]
 
-#[cfg(any(windows, feature = "documentation"))]
+#[cfg(any(windows, rustdoc))]
 #[doc(cfg(windows))]
 /// The application's icon in the notification area (a.k.a. system tray).
 ///
@@ -39,4 +43,4 @@ pub struct Icon {
 ```
 
 [#43781]: https://github.com/rust-lang/rust/issues/43781
-[#43348]: https://github.com/rust-lang/rust/issues/43348
\ No newline at end of file
+[#43348]: https://github.com/rust-lang/rust/issues/43348
diff --git a/src/libcore/macros.rs b/src/libcore/macros.rs
index 5b3b2d1635688..0032bedc7ed1d 100644
--- a/src/libcore/macros.rs
+++ b/src/libcore/macros.rs
@@ -541,7 +541,7 @@ macro_rules! unimplemented {
 /// into libsyntax itself.
 ///
 /// For more information, see documentation for `std`'s macros.
-#[cfg(dox)]
+#[cfg(rustdoc)]
 mod builtin {
 
     /// Unconditionally causes compilation to fail with the given error message when encountered.
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index 279151eb26def..feae724b55d09 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -466,7 +466,8 @@ fn main_args(args: &[String]) -> isize {
 
     let output = matches.opt_str("o").map(|s| PathBuf::from(&s));
     let css_file_extension = matches.opt_str("e").map(|s| PathBuf::from(&s));
-    let cfgs = matches.opt_strs("cfg");
+    let mut cfgs = matches.opt_strs("cfg");
+    cfgs.push("rustdoc".to_string());
 
     if let Some(ref p) = css_file_extension {
         if !p.is_file() {
@@ -643,7 +644,8 @@ where R: 'static + Send,
     for s in &matches.opt_strs("L") {
         paths.add_path(s, ErrorOutputType::default());
     }
-    let cfgs = matches.opt_strs("cfg");
+    let mut cfgs = matches.opt_strs("cfg");
+    cfgs.push("rustdoc".to_string());
     let triple = matches.opt_str("target").map(|target| {
         if target.ends_with(".json") {
             TargetTriple::TargetPath(PathBuf::from(target))
diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index 6945a41a5e73b..b649ec2340e93 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -309,7 +309,7 @@ macro_rules! assert_approx_eq {
 /// These macros do not have any corresponding definition with a `macro_rules!`
 /// macro, but are documented here. Their implementations can be found hardcoded
 /// into libsyntax itself.
-#[cfg(dox)]
+#[cfg(rustdoc)]
 mod builtin {
 
     /// Unconditionally causes compilation to fail with the given error message when encountered.
diff --git a/src/libstd/os/mod.rs b/src/libstd/os/mod.rs
index c384ec9168ac4..6bc186e796666 100644
--- a/src/libstd/os/mod.rs
+++ b/src/libstd/os/mod.rs
@@ -14,7 +14,7 @@
 #![allow(missing_docs, bad_style, missing_debug_implementations)]
 
 cfg_if! {
-    if #[cfg(dox)] {
+    if #[cfg(rustdoc)] {
 
         // When documenting libstd we want to show unix/windows/linux modules as
         // these are the "main modules" that are used across platforms. This
diff --git a/src/libstd/sys/mod.rs b/src/libstd/sys/mod.rs
index c44db3b107224..61e4ce66eec0f 100644
--- a/src/libstd/sys/mod.rs
+++ b/src/libstd/sys/mod.rs
@@ -57,7 +57,7 @@ cfg_if! {
 // then later used in the `std::os` module when documenting, for example,
 // Windows when we're compiling for Linux.
 
-#[cfg(dox)]
+#[cfg(rustdoc)]
 cfg_if! {
     if #[cfg(any(unix, target_os = "redox"))] {
         // On unix we'll document what's already available
@@ -77,7 +77,7 @@ cfg_if! {
     }
 }
 
-#[cfg(dox)]
+#[cfg(rustdoc)]
 cfg_if! {
     if #[cfg(windows)] {
         // On windows we'll just be documenting what's already available
diff --git a/src/libstd/sys/unix/mod.rs b/src/libstd/sys/unix/mod.rs
index c738003caf1d9..a631ef5ec5cbd 100644
--- a/src/libstd/sys/unix/mod.rs
+++ b/src/libstd/sys/unix/mod.rs
@@ -13,22 +13,22 @@
 use io::{self, ErrorKind};
 use libc;
 
-#[cfg(any(dox, target_os = "linux"))] pub use os::linux as platform;
-
-#[cfg(all(not(dox), target_os = "android"))]   pub use os::android as platform;
-#[cfg(all(not(dox), target_os = "bitrig"))]    pub use os::bitrig as platform;
-#[cfg(all(not(dox), target_os = "dragonfly"))] pub use os::dragonfly as platform;
-#[cfg(all(not(dox), target_os = "freebsd"))]   pub use os::freebsd as platform;
-#[cfg(all(not(dox), target_os = "haiku"))]     pub use os::haiku as platform;
-#[cfg(all(not(dox), target_os = "ios"))]       pub use os::ios as platform;
-#[cfg(all(not(dox), target_os = "macos"))]     pub use os::macos as platform;
-#[cfg(all(not(dox), target_os = "netbsd"))]    pub use os::netbsd as platform;
-#[cfg(all(not(dox), target_os = "openbsd"))]   pub use os::openbsd as platform;
-#[cfg(all(not(dox), target_os = "solaris"))]   pub use os::solaris as platform;
-#[cfg(all(not(dox), target_os = "emscripten"))] pub use os::emscripten as platform;
-#[cfg(all(not(dox), target_os = "fuchsia"))]   pub use os::fuchsia as platform;
-#[cfg(all(not(dox), target_os = "l4re"))]      pub use os::linux as platform;
-#[cfg(all(not(dox), target_os = "hermit"))]    pub use os::hermit as platform;
+#[cfg(any(rustdoc, target_os = "linux"))] pub use os::linux as platform;
+
+#[cfg(all(not(rustdoc), target_os = "android"))]   pub use os::android as platform;
+#[cfg(all(not(rustdoc), target_os = "bitrig"))]    pub use os::bitrig as platform;
+#[cfg(all(not(rustdoc), target_os = "dragonfly"))] pub use os::dragonfly as platform;
+#[cfg(all(not(rustdoc), target_os = "freebsd"))]   pub use os::freebsd as platform;
+#[cfg(all(not(rustdoc), target_os = "haiku"))]     pub use os::haiku as platform;
+#[cfg(all(not(rustdoc), target_os = "ios"))]       pub use os::ios as platform;
+#[cfg(all(not(rustdoc), target_os = "macos"))]     pub use os::macos as platform;
+#[cfg(all(not(rustdoc), target_os = "netbsd"))]    pub use os::netbsd as platform;
+#[cfg(all(not(rustdoc), target_os = "openbsd"))]   pub use os::openbsd as platform;
+#[cfg(all(not(rustdoc), target_os = "solaris"))]   pub use os::solaris as platform;
+#[cfg(all(not(rustdoc), target_os = "emscripten"))] pub use os::emscripten as platform;
+#[cfg(all(not(rustdoc), target_os = "fuchsia"))]   pub use os::fuchsia as platform;
+#[cfg(all(not(rustdoc), target_os = "l4re"))]      pub use os::linux as platform;
+#[cfg(all(not(rustdoc), target_os = "hermit"))]    pub use os::hermit as platform;
 
 pub use self::rand::hashmap_random_keys;
 pub use libc::strlen;
diff --git a/src/libstd/sys/windows/c.rs b/src/libstd/sys/windows/c.rs
index e514a56dcc436..10f48c3c308a7 100644
--- a/src/libstd/sys/windows/c.rs
+++ b/src/libstd/sys/windows/c.rs
@@ -794,7 +794,7 @@ pub struct FLOATING_SAVE_AREA {
 // will not appear in the final documentation. This should be also defined for
 // other architectures supported by Windows such as ARM, and for historical
 // interest, maybe MIPS and PowerPC as well.
-#[cfg(all(dox, not(any(target_arch = "x86_64", target_arch = "x86", target_arch = "aarch64"))))]
+#[cfg(all(rustdoc, not(any(target_arch = "x86_64", target_arch = "x86", target_arch = "aarch64"))))]
 pub enum CONTEXT {}
 
 #[cfg(target_arch = "aarch64")]
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 6dd788bf6e2ac..7f051ac3ebcc0 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -1148,6 +1148,7 @@ const GATED_CFGS: &[(&str, &str, fn(&Features) -> bool)] = &[
     ("target_vendor", "cfg_target_vendor", cfg_fn!(cfg_target_vendor)),
     ("target_thread_local", "cfg_target_thread_local", cfg_fn!(cfg_target_thread_local)),
     ("target_has_atomic", "cfg_target_has_atomic", cfg_fn!(cfg_target_has_atomic)),
+    ("rustdoc", "doc_cfg", cfg_fn!(doc_cfg)),
 ];
 
 #[derive(Debug)]
diff --git a/src/test/ui/feature-gate-doc_cfg-cfg-rustdoc.rs b/src/test/ui/feature-gate-doc_cfg-cfg-rustdoc.rs
new file mode 100644
index 0000000000000..6207d99dc36aa
--- /dev/null
+++ b/src/test/ui/feature-gate-doc_cfg-cfg-rustdoc.rs
@@ -0,0 +1,14 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[cfg(rustdoc)] //~ ERROR: `cfg(rustdoc)` is experimental and subject to change
+pub struct SomeStruct;
+
+fn main() {}
diff --git a/src/test/ui/feature-gate-doc_cfg-cfg-rustdoc.stderr b/src/test/ui/feature-gate-doc_cfg-cfg-rustdoc.stderr
new file mode 100644
index 0000000000000..be2c263af042d
--- /dev/null
+++ b/src/test/ui/feature-gate-doc_cfg-cfg-rustdoc.stderr
@@ -0,0 +1,11 @@
+error[E0658]: `cfg(rustdoc)` is experimental and subject to change (see issue #43781)
+  --> $DIR/feature-gate-doc_cfg-cfg-rustdoc.rs:11:7
+   |
+LL | #[cfg(rustdoc)] //~ ERROR: `cfg(rustdoc)` is experimental and subject to change
+   |       ^^^^^^^
+   |
+   = help: add #![feature(doc_cfg)] to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.