2 files changed, 4 insertions, 1 deletions
diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index e38a574ca23..7a684c89fe3 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -1171,7 +1171,6 @@ def bootstrap(help_triggered):
     env = os.environ.copy()
     env["BOOTSTRAP_PARENT_ID"] = str(os.getpid())
     env["BOOTSTRAP_PYTHON"] = sys.executable
-    env["RUSTC_BOOTSTRAP"] = '1'
     if build.rustc_commit is not None:
         env["BOOTSTRAP_DOWNLOAD_RUSTC"] = '1'
     run(args, env=env, verbose=build.verbose, is_bootstrap=True)
diff --git a/src/bootstrap/doc.rs b/src/bootstrap/doc.rs
index fcef784d2d1..be6655ddb61 100644
--- a/src/bootstrap/doc.rs
+++ b/src/bootstrap/doc.rs
@@ -881,6 +881,10 @@ impl Step for RustcBook {
         if self.validate {
             cmd.arg("--validate");
         }
+        if !builder.unstable_features() {
+            // We need to validate nightly features, even on the stable channel.
+            cmd.env("RUSTC_BOOTSTRAP", "1");
+        }
         // If the lib directories are in an unusual location (changed in
         // config.toml), then this needs to explicitly update the dylib search
         // path.