diff --git a/utils/swift_build_support/swift_build_support/products/llvm.py b/utils/swift_build_support/swift_build_support/products/llvm.py
index 6fc15415e40f5..92721fb45c797 100644
--- a/utils/swift_build_support/swift_build_support/products/llvm.py
+++ b/utils/swift_build_support/swift_build_support/products/llvm.py
@@ -313,7 +313,7 @@ def build(self, host_target):
             llvm_cmake_options.define(
                 'SANITIZER_COMMON_LINK_FLAGS:STRING', '-Wl,-z,undefs')
 
-        builtins_runtimes_target_for_darwin = 'arm64-apple-darwin'
+        builtins_runtimes_target_for_darwin = f'{arch}-apple-darwin'
         if system() == "Darwin":
             llvm_cmake_options.define(
                 f'BUILTINS_{builtins_runtimes_target_for_darwin}_'