diff --git a/tools/ci_build/build.py b/tools/ci_build/build.py
index 7f292373b0977..f6e71b5701b7e 100644
--- a/tools/ci_build/build.py
+++ b/tools/ci_build/build.py
@@ -1205,7 +1205,7 @@ def generate_build_tree(
                 raise BuildError("unknown python arch")
         elif is_macOS():
             for kvp in cmake_extra_args:
-                key, value = s.split("=")
+                key, value = kvp.split("=")
                 if key == "CMAKE_OSX_ARCHITECTURES" and len(value.split(";")) == 2:
                     triplet = "universal2-osx"
         if triplet: