diff --git a/ext/digest/extconf.rb b/ext/digest/extconf.rb
index aad3216..2b3df12 100755
--- a/ext/digest/extconf.rb
+++ b/ext/digest/extconf.rb
@@ -17,6 +17,9 @@ def have_func!(header, *args)
   exit 1 unless have_func(*args, header)
 end
 
+cflags '-std=c11'
+cflags '-Wall'
+cflags '-Wextra'
 cflags '-fvisibility=hidden'
 
 have_header! 'ruby/digest.h'