diff --git a/rust/toolchain.bzl b/rust/toolchain.bzl
index d91248a8b3..d25937fa2e 100644
--- a/rust/toolchain.bzl
+++ b/rust/toolchain.bzl
@@ -295,6 +295,7 @@ rust_toolchain = rule(
         ),
         "rustc_lib": attr.label(
             doc = "The libraries used by rustc during compilation.",
+            cfg = "exec",
         ),
         "rustc_srcs": attr.label(
             doc = "The source code of rustc.",