diff --git a/pkgs/build-support/rust/fetchcargo.nix b/pkgs/build-support/rust/fetchcargo.nix
index 01e410c8bf8e..7a0ba38dce71 100644
--- a/pkgs/build-support/rust/fetchcargo.nix
+++ b/pkgs/build-support/rust/fetchcargo.nix
@@ -18,9 +18,9 @@ let cargo-vendor-normalise = stdenv.mkDerivation {
 };
 in
 { name ? "cargo-deps"
-, src
-, srcs
-, patches
+, src ? null
+, srcs ? []
+, patches ? []
 , sourceRoot
 , sha256
 , cargoUpdateHook ? ""
diff --git a/pkgs/development/compilers/rust/default.nix b/pkgs/development/compilers/rust/default.nix
index 75104ac7ad58..60e31c6def47 100644
--- a/pkgs/development/compilers/rust/default.nix
+++ b/pkgs/development/compilers/rust/default.nix
@@ -19,17 +19,17 @@
     }.${cpu.name} or cpu.name;
   in "${cpu_}-${vendor.name}-${kernel.name}${lib.optionalString (abi.name != "unknown") "-${abi.name}"}";
 
-  makeRustPlatform = { rustc, cargo, ... }: {
+  makeRustPlatform = { rustc, cargo, ... }: rec {
     rust = {
       inherit rustc cargo;
     };
 
-    buildRustPackage = callPackage ../../../build-support/rust {
-      inherit rustc cargo;
+    fetchcargo = buildPackages.callPackage ../../../build-support/rust/fetchcargo.nix {
+      inherit cargo;
+    };
 
-      fetchcargo = buildPackages.callPackage ../../../build-support/rust/fetchcargo.nix {
-        inherit cargo;
-      };
+    buildRustPackage = callPackage ../../../build-support/rust {
+      inherit rustc cargo fetchcargo;
     };
 
     rustcSrc = callPackage ./rust-src.nix {