diff --git a/src/cargo/core/compiler/custom_build.rs b/src/cargo/core/compiler/custom_build.rs
index 16a2f4888b6..d7e6aadc306 100644
--- a/src/cargo/core/compiler/custom_build.rs
+++ b/src/cargo/core/compiler/custom_build.rs
@@ -460,6 +460,11 @@ fn build_work(build_runner: &mut BuildRunner<'_, '_>, unit: &Unit) -> CargoResul
     // sorts of variables need to be discovered at that time.
     let lib_deps = dependencies
         .iter()
+        // We allow std dependencies to propagate metadata between other std dependencies but
+        // not to non-std crates. Non-std crates can propagate metadata to other non-std crates.
+        // We enforce a boundary between std and non-std crates. This may be lifted in the
+        // future but for now we are being conservative.
+        .filter(|dep| dep.unit.is_std == unit.is_std)
         .filter_map(|dep| {
             if dep.unit.mode.is_run_custom_build() {
                 let dep_metadata = build_runner.get_run_build_script_metadata(&dep.unit);