Index: src/org/jruby/ext/posix/POSIXFactory.java
===================================================================
--- src/org/jruby/ext/posix/POSIXFactory.java	(revision 213)
+++ src/org/jruby/ext/posix/POSIXFactory.java	(working copy)
@@ -87,7 +87,7 @@
         Map<Object, Object> options = new HashMap<Object, Object>();
         options.put(com.sun.jna.Library.OPTION_FUNCTION_MAPPER, new WindowsLibCFunctionMapper());
 
-        return new WindowsPOSIX(name, loadLibC(name, LibC.class, options), handler);
+        return new WindowsPOSIX(name, loadLibC(name, WindowsLibC.class, options), handler);
     }
 
     public static LibC loadLibC(String libraryName, Class<?> libCClass, Map<Object, Object> options) {
Index: src/org/jruby/ext/posix/WindowsLibCFunctionMapper.java
===================================================================
--- src/org/jruby/ext/posix/WindowsLibCFunctionMapper.java	(revision 213)
+++ src/org/jruby/ext/posix/WindowsLibCFunctionMapper.java	(working copy)
@@ -23,6 +23,7 @@
         methodNameMap.put("stat", "_stat64");
         methodNameMap.put("mkdir", "_mkdir");
         methodNameMap.put("umask", "_umask");
+	methodNameMap.put("isatty", "_isatty");
     }
   
     public String getFunctionName(NativeLibrary library, Method method) {
Index: src/org/jruby/ext/posix/JavaLibCHelper.java
===================================================================
--- src/org/jruby/ext/posix/JavaLibCHelper.java	(revision 213)
+++ src/org/jruby/ext/posix/JavaLibCHelper.java	(working copy)
@@ -53,11 +53,14 @@
     public static final int STDERR = 2;
 
     POSIXHandler handler;
-    Field field;
+    Field fdField, handleField;
 
     public JavaLibCHelper(POSIXHandler handler) {
         this.handler = handler;
-        this.field = FieldAccess.getProtectedField(FileDescriptor.class, "fd");
+	this.handleField = FieldAccess.getProtectedField(FileDescriptor.class,
+							 "handle");
+        this.fdField = FieldAccess.getProtectedField(FileDescriptor.class,
+						     "fd");
     }
     
     public int chmod(String filename, int mode) {
@@ -78,10 +81,9 @@
     }
 
     public int getfd(FileDescriptor descriptor) {
-        if (descriptor == null || field == null) return -1;
-        
+        if (descriptor == null || fdField == null) return -1;
         try {
-            return field.getInt(descriptor);
+            return fdField.getInt(descriptor);
         } catch (SecurityException e) {
         } catch (IllegalArgumentException e) {
         } catch (IllegalAccessException e) {
@@ -90,6 +92,18 @@
         return -1;
     }
 
+    public long gethandle(FileDescriptor descriptor) {
+        if (descriptor == null || handleField == null) return -1;
+        try {
+            return handleField.getLong(descriptor);
+        } catch (SecurityException e) {
+        } catch (IllegalArgumentException e) {
+        } catch (IllegalAccessException e) {
+        }
+
+        return -1;
+    }
+
     public String getlogin() {
         return System.getProperty("user.name");
     }
Index: src/org/jruby/ext/posix/WindowsPOSIX.java
===================================================================
--- src/org/jruby/ext/posix/WindowsPOSIX.java	(revision 213)
+++ src/org/jruby/ext/posix/WindowsPOSIX.java	(working copy)
@@ -220,8 +220,8 @@
 
     @Override
     public boolean isatty(FileDescriptor fd) {
-        return (fd == FileDescriptor.in
-                || fd == FileDescriptor.out
-                || fd == FileDescriptor.err);
+	int handle = (int)helper.gethandle(fd);
+	int crtfd = ((WindowsLibC)libc)._open_osfhandle(handle, 0/*_O_RDONLY*/);
+	return libc.isatty(crtfd) != 0;
     }
 }
Index: src/org/jruby/ext/posix/WindowsLibC.java
===================================================================
--- src/org/jruby/ext/posix/WindowsLibC.java	(revision 213)
+++ src/org/jruby/ext/posix/WindowsLibC.java	(working copy)
@@ -1,4 +1,5 @@
 package org.jruby.ext.posix;
 
-public interface WindowsLibC extends POSIX {
+public interface WindowsLibC extends LibC {
+    public int _open_osfhandle(int handle, int flags);
 }