diff --git a/subprojects/bahaghari/lib/default.nix b/subprojects/bahaghari/lib/default.nix
index f247b026..7f370a92 100644
--- a/subprojects/bahaghari/lib/default.nix
+++ b/subprojects/bahaghari/lib/default.nix
@@ -45,7 +45,7 @@ pkgs.lib.makeExtensible
 
     inherit (self.trivial) importYAML toYAML toBaseDigitsWithGlyphs
       generateGlyphSet generateConversionTable generateBaseDigitType clamp
-      isNumber scale;
+      isNumber scale optionalNull;
 
     inherit (self.hex) isHexString;
     inherit (self.math) abs pow percentage factorial floor ceil round round'