diff --git a/nix/buildLisp/default.nix b/nix/buildLisp/default.nix
index 58ba492a0..3203206fb 100644
--- a/nix/buildLisp/default.nix
+++ b/nix/buildLisp/default.nix
@@ -116,6 +116,7 @@ let
     lispDeps = allDeps deps;
   in runCommandNoCC "${name}-cllib" {
     LD_LIBRARY_PATH = lib.makeLibraryPath lispNativeDeps;
+    LANG = "C.UTF-8";
   } ''
     ${sbcl}/bin/sbcl --script ${genCompileLisp srcs lispDeps}