diff --git a/pkgs/os-specific/linux/kernel/manual-config.nix b/pkgs/os-specific/linux/kernel/manual-config.nix
index 460a5b0a52b7..38eda04ecb77 100644
--- a/pkgs/os-specific/linux/kernel/manual-config.nix
+++ b/pkgs/os-specific/linux/kernel/manual-config.nix
@@ -245,11 +245,13 @@ lib.makeOverridable (
           rust-bindgen-unwrapped
         ];
 
-        RUST_LIB_SRC = lib.optionalString withRust rustPlatform.rustLibSrc;
+        env = {
+          RUST_LIB_SRC = lib.optionalString withRust rustPlatform.rustLibSrc;
 
-        # avoid leaking Rust source file names into the final binary, which adds
-        # a false dependency on rust-lib-src on targets with uncompressed kernels
-        KRUSTFLAGS = lib.optionalString withRust "--remap-path-prefix ${rustPlatform.rustLibSrc}=/";
+          # avoid leaking Rust source file names into the final binary, which adds
+          # a false dependency on rust-lib-src on targets with uncompressed kernels
+          KRUSTFLAGS = lib.optionalString withRust "--remap-path-prefix ${rustPlatform.rustLibSrc}=/";
+        };
 
         patches =
           # kernelPatches can contain config changes and no actual patch