diff --git a/compiler/rustc_feature/src/lib.rs b/compiler/rustc_feature/src/lib.rs
index 8e2a13a6c0a..93d16716346 100644
--- a/compiler/rustc_feature/src/lib.rs
+++ b/compiler/rustc_feature/src/lib.rs
@@ -83,7 +83,8 @@ impl UnstableFeatures {
     /// Otherwise, only `RUSTC_BOOTSTRAP=1` will work.
     pub fn from_environment(krate: Option<&str>) -> Self {
         // `true` if this is a feature-staged build, i.e., on the beta or stable channel.
-        let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
+        let disable_unstable_features =
+            option_env!("CFG_DISABLE_UNSTABLE_FEATURES").map(|s| s != "0").unwrap_or(false);
         // Returns whether `krate` should be counted as unstable
         let is_unstable_crate = |var: &str| {
             krate.map_or(false, |name| var.split(',').any(|new_krate| new_krate == name))
diff --git a/library/test/src/cli.rs b/library/test/src/cli.rs
index 796796e07a9..9d22ebbee87 100644
--- a/library/test/src/cli.rs
+++ b/library/test/src/cli.rs
@@ -309,7 +309,8 @@ fn parse_opts_impl(matches: getopts::Matches) -> OptRes {
 // FIXME: Copied from librustc_ast until linkage errors are resolved. Issue #47566
 fn is_nightly() -> bool {
     // Whether this is a feature-staged build, i.e., on the beta or stable channel
-    let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
+    let disable_unstable_features =
+        option_env!("CFG_DISABLE_UNSTABLE_FEATURES").map(|s| s != "0").unwrap_or(false);
     // Whether we should enable unstable features for bootstrapping
     let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();