diff --git a/configure.in b/configure.in
index 3a1999c..e054841 100644
--- a/configure.in
+++ b/configure.in
@@ -1101,6 +1101,7 @@ AC_CHECK_HEADERS(limits.h sys/file.h sys/ioctl.h sys/syscall.h\
 		 sys/mkdev.h sys/utime.h xti.h netinet/in_systm.h float.h ieeefp.h \
 		 ucontext.h intrinsics.h langinfo.h locale.h sys/sendfile.h time.h \
 		 net/socket.h sys/socket.h)
+AC_CHECK_HEADERS_ONCE([windows.h])
 
 dnl Check additional types.
 RUBY_CHECK_SIZEOF(rlim_t, [int long "long long"], [], [
diff --git a/test/fiddle/test_fiddle.rb b/test/fiddle/test_fiddle.rb
index fa19aaf..625aaf9 100644
--- a/test/fiddle/test_fiddle.rb
+++ b/test/fiddle/test_fiddle.rb
@@ -16,4 +16,14 @@ class TestFiddle < Fiddle::TestCase
       assert_equal(DL.const_get(name), Fiddle.const_get(name))
     end
   end
+
+  def test_windows_constant
+    require 'rbconfig'
+    if RbConfig::CONFIG['host_os'] =~ /mswin|mingw/
+      assert Fiddle::WINDOWS, "Fiddle::WINDOWS should be 'true' on Windows platforms"
+    else
+      refute Fiddle::WINDOWS, "Fiddle::WINDOWS should be 'false' on non-Windows platforms"
+    end
+  end
+
 end
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index 4e2a069..937e778 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -450,6 +450,7 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 !endif
 #define RT_VER $(RT_VER)
 #define STDC_HEADERS 1
+#define HAVE_WINDOWS_H 1
 #define HAVE_SYS_TYPES_H 1
 #define HAVE_SYS_STAT_H 1
 #define HAVE_STDLIB_H 1