diff --git a/pkgs/development/libraries/x265/default.nix b/pkgs/development/libraries/x265/default.nix
index 92f7f11170f6..b63b0101d54b 100644
--- a/pkgs/development/libraries/x265/default.nix
+++ b/pkgs/development/libraries/x265/default.nix
@@ -35,8 +35,7 @@ let
     (mkFlag vtuneSupport "ENABLE_VTUNE")
     (mkFlag werrorSupport "WARNINGS_AS_ERRORS")
     # Potentially riscv cross could be fixed by providing the correct CMAKE_SYSTEM_PROCESSOR flag
-    (mkFlag (with stdenv; !(isCross && hostPlatform.isRiscV || isDarwin && isAarch64)) "ENABLE_ASSEMBLY")
-  ];
+  ] ++ lib.optional (isCross && stdenv.hostPlatform.isRiscV) "-DENABLE_ASSEMBLY=OFF";
 
   cmakeStaticLibFlags = [
     "-DHIGH_BIT_DEPTH=ON"