diff --git a/buildutils/build.py b/buildutils/build.py
index 17b487d..297b470 100644
--- a/buildutils/build.py
+++ b/buildutils/build.py
@@ -14,7 +14,7 @@ def build_libcapnp(bundle_dir, build_dir, verbose=False):
     if verbose:
       stdout = None
     cxxflags = os.environ.get('CXXFLAGS', '')
-    os.environ['CXXFLAGS'] = cxxflags + ' -fPIC'
+    os.environ['CXXFLAGS'] = cxxflags + ' -fPIC -O2 -DNDEBUG'
     conf = subprocess.Popen(['./configure', '--disable-shared', '--prefix', build_dir], cwd=capnp_dir, stdout=stdout)
     returncode = conf.wait()
     if returncode != 0: