diff --git a/pkgs/development/compilers/llvm/common/libcxx/default.nix b/pkgs/development/compilers/llvm/common/libcxx/default.nix
index d4b727bd50d2..453013cdbd27 100644
--- a/pkgs/development/compilers/llvm/common/libcxx/default.nix
+++ b/pkgs/development/compilers/llvm/common/libcxx/default.nix
@@ -44,6 +44,8 @@ let
       cp -r ${monorepoSrc}/llvm/utils "$out/llvm"
     '' + (lib.optionalString (lib.versionAtLeast release_version "14") ''
       cp -r ${monorepoSrc}/third-party "$out"
+    '') + (lib.optionalString (lib.versionAtLeast release_version "20") ''
+      cp -r ${monorepoSrc}/libc "$out"
     '') + ''
       cp -r ${monorepoSrc}/runtimes "$out"
     '' + (lib.optionalString (cxxabi == null) ''