diff --git a/Formula/libfido2.rb b/Formula/libfido2.rb
index fe2be86bbd3..5b08a68401f 100644
--- a/Formula/libfido2.rb
+++ b/Formula/libfido2.rb
@@ -47,7 +47,7 @@ class Libfido2 < Formula
       fido_dev_info_free(&devlist, max_devices);
     }
     EOF
-    system ENV.cc, "-std=c99", "test.c", "-I#{include}", "-I#{Formula["openssl@1.1"].include}", "-o", "test",
+    system ENV.cc, "test.c", "-I#{include}", "-I#{Formula["openssl@1.1"].include}", "-o", "test",
                    "-L#{lib}", "-lfido2"
     system "./test"
   end