diff --git a/tools/run_tests/helper_scripts/build_python.sh b/tools/run_tests/helper_scripts/build_python.sh
index 52f9729e260..87c16a2ec4f 100755
--- a/tools/run_tests/helper_scripts/build_python.sh
+++ b/tools/run_tests/helper_scripts/build_python.sh
@@ -122,7 +122,7 @@ export LANG=en_US.UTF-8
 
 # Allow build_ext to build C/C++ files in parallel
 # by enabling a monkeypatch. It speeds up the build a lot.
-DEFAULT_PARALLEL_JOBS=`nproc` || DEFAULT_PARALLEL_JOBS=4
+DEFAULT_PARALLEL_JOBS=$(nproc) || DEFAULT_PARALLEL_JOBS=4
 export GRPC_PYTHON_BUILD_EXT_COMPILER_JOBS=${GRPC_PYTHON_BUILD_EXT_COMPILER_JOBS:-$DEFAULT_PARALLEL_JOBS}
 
 # If ccache is available on Linux, use it.