diff --git a/ext/fiddle/win32/libffi-config.rb b/ext/fiddle/win32/libffi-config.rb
index 1a750334..8e8069a9 100755
--- a/ext/fiddle/win32/libffi-config.rb
+++ b/ext/fiddle/win32/libffi-config.rb
@@ -23,7 +23,7 @@
   end
 end
 
-IO.foreach("#{srcdir}/configure.ac") do |line|
+File.foreach("#{srcdir}/configure.ac") do |line|
   if /^AC_INIT\((.*)\)/ =~ line
     version = $1.split(/,\s*/)[1]
     version.gsub!(/\A\[|\]\z/, '')