diff --git a/crates/ide-assists/Cargo.toml b/crates/ide-assists/Cargo.toml
index df52562b6a..2a14fbe1e0 100644
--- a/crates/ide-assists/Cargo.toml
+++ b/crates/ide-assists/Cargo.toml
@@ -34,5 +34,8 @@ expect-test = "1.4.0"
 test-utils.workspace = true
 test-fixture.workspace = true
 
+[features]
+in-rust-tree = []
+
 [lints]
 workspace = true
diff --git a/crates/ide-assists/src/lib.rs b/crates/ide-assists/src/lib.rs
index b2ccd1fde8..c98655b423 100644
--- a/crates/ide-assists/src/lib.rs
+++ b/crates/ide-assists/src/lib.rs
@@ -58,6 +58,8 @@
 //! See also this post:
 //! <https://rust-analyzer.github.io/blog/2020/09/28/how-to-make-a-light-bulb.html>
 
+#![cfg_attr(feature = "in-rust-tree", feature(rustc_private))]
+
 mod assist_config;
 mod assist_context;
 #[cfg(test)]
diff --git a/crates/mbe/src/lib.rs b/crates/mbe/src/lib.rs
index dd71e46db3..ca10a2be27 100644
--- a/crates/mbe/src/lib.rs
+++ b/crates/mbe/src/lib.rs
@@ -6,6 +6,8 @@
 //! The tests for this functionality live in another crate:
 //! `hir_def::macro_expansion_tests::mbe`.
 
+#![cfg_attr(feature = "in-rust-tree", feature(rustc_private))]
+
 #[cfg(not(feature = "in-rust-tree"))]
 extern crate ra_ap_rustc_lexer as rustc_lexer;
 #[cfg(feature = "in-rust-tree")]