diff --git a/pkgs/by-name/ac/ac-library/package.nix b/pkgs/by-name/ac/ac-library/package.nix
index 2123dd086cb1..b112b8128a81 100644
--- a/pkgs/by-name/ac/ac-library/package.nix
+++ b/pkgs/by-name/ac/ac-library/package.nix
@@ -60,6 +60,7 @@ stdenv.mkDerivation (finalAttrs: {
   env = {
     NIX_CFLAGS_COMPILE = toString [
       "-Wno-error=array-bounds"
+      "-Wno-character-conversion"
     ];
   };