diff --git a/ci/config.mk.clang.sed b/ci/config.mk.clang.sed
index da6044d..2e27c7c 100644
--- a/ci/config.mk.clang.sed
+++ b/ci/config.mk.clang.sed
@@ -1,2 +1,2 @@
 /^CFLAGS[[:blank:]]*=/s/$/ -Wno-error=missing-field-initializers/
-/^RUBY_CFLAGS[[:blank:]]*=/s/$/ -Wno-error=unknown-attributes -Wno-error=ignored-attributes/
+/^RUBY_CFLAGS[[:blank:]]*=/s/$/ -Wno-error=unknown-attributes -Wno-error=ignored-attributes -fms-extensions/