diff --git a/third_party/lisp/sb-posix.nix b/third_party/lisp/sb-posix.nix
new file mode 100644
index 000000000..5fc65d3f5
--- /dev/null
+++ b/third_party/lisp/sb-posix.nix
@@ -0,0 +1,10 @@
+# SB-POSIX is an SBCL component. This package just forces it to be
+# loaded.
+{ pkgs, ... }:
+
+with pkgs;
+
+nix.buildLisp.library {
+  name = "sb-posix";
+  srcs = lib.singleton (builtins.toFile "sb-posix.lisp" "(require 'sb-posix)");
+}