diff --git a/var/spack/repos/builtin/packages/py-grpcio/package.py b/var/spack/repos/builtin/packages/py-grpcio/package.py
index 18981f20e458e67d1198eaa6c41e9fa5afbbac71..e40d3c0532c91c7ee30bdf90e1b7311cc45788e7 100644
--- a/var/spack/repos/builtin/packages/py-grpcio/package.py
+++ b/var/spack/repos/builtin/packages/py-grpcio/package.py
@@ -29,3 +29,7 @@ def setup_build_environment(self, env):
         env.set('GRPC_PYTHON_BUILD_SYSTEM_OPENSSL', True)
         env.set('GRPC_PYTHON_BUILD_SYSTEM_ZLIB', True)
         env.set('GRPC_PYTHON_BUILD_SYSTEM_CARES', True)
+
+    def patch(self):
+        if self.spec.satisfies('%fj'):
+            filter_file("-std=gnu99", "", "setup.py")