diff --git a/setup.py b/setup.py
index b7a24c47..85e53ff4 100644
--- a/setup.py
+++ b/setup.py
@@ -97,7 +97,7 @@ def build_extensions(self):
             env = os.environ.copy()
             env["PYTHON"] = sys.executable
             env["PYTHON_INCLUDE"] = f'-I{sysconfig.get_path("include")}'
-            env["CXXFLAGS"] = "-O3 -Bstatic -Bdynamic -std=c++17"
+            env["CXXFLAGS"] = "-O3 -Bstatic -Bdynamic -std=c++17 " + env.get("CXXFLAGS", "")
             env["LDFLAGS"] = env.get("LDFLAGS", "") + f" -Wl,-rpath,{_rpath}"
             env["ORIGIN"] = "$ORIGIN"  # if evaluated, it will still be '$ORIGIN'