diff --git a/ext/digest/extconf.rb b/ext/digest/extconf.rb
index 2b3df12..028f628 100644
--- a/ext/digest/extconf.rb
+++ b/ext/digest/extconf.rb
@@ -5,7 +5,7 @@
 
 def cflags(*args)
   args.each do |str|
-    $CFLAGS += " #{str.shellescape} "
+    $CFLAGS += (ENV['OS'] == "Windows_NT") ? " #{str} " : " #{str.shellescape} "
   end
 end