diff --git a/pkgs/os-specific/darwin/apple-source-releases/Libsystem/default.nix b/pkgs/os-specific/darwin/apple-source-releases/Libsystem/default.nix
index 206f46125b9b..af37143835c5 100644
--- a/pkgs/os-specific/darwin/apple-source-releases/Libsystem/default.nix
+++ b/pkgs/os-specific/darwin/apple-source-releases/Libsystem/default.nix
@@ -59,7 +59,7 @@ appleDerivation' stdenv {
       (cd $dep/include && find . -name '*.h' | copyHierarchy $out/include)
     done
 
-    (cd ${buildPackages.darwin.cctools.dev}/include/mach-o && find . -name '*.h' | copyHierarchy $out/include/mach-o)
+    (cd ${lib.getDev buildPackages.darwin.cctools}/include/mach-o && find . -name '*.h' | copyHierarchy $out/include/mach-o)
 
     for header in pthread.h pthread_impl.h pthread_spis.h sched.h; do
       ln -s "$out/include/pthread/$header" "$out/include/$header"
@@ -142,7 +142,7 @@ appleDerivation' stdenv {
       $out/lib
 
     substituteInPlace $out/lib/libSystem.B.tbd \
-      --replace "/usr/lib/system/" "$out/lib/system/"
+      --replace-fail "/usr/lib/system/" "$out/lib/system/"
     ln -s libSystem.B.tbd $out/lib/libSystem.tbd
 
     # Set up links to pretend we work like a conventional unix (Apple's design, not mine!)