diff --git a/ext/puma_http11/extconf.rb b/ext/puma_http11/extconf.rb
index a0edd839ec..feb812d8a6 100644
--- a/ext/puma_http11/extconf.rb
+++ b/ext/puma_http11/extconf.rb
@@ -1,7 +1,7 @@
 require 'mkmf'
 
 dir_config("puma_http11")
-if RUBY_PLATFORM[/mingw32/]
+if $mingw && RUBY_VERSION >= '2.4'
   append_cflags '-D_FORTIFY_SOURCE=2'
   append_ldflags '-fstack-protector'
   have_library 'ssp'