diff --git a/Include/fileobject.h b/Include/fileobject.h
index 56cf40a..1fed47b 100644
--- a/Include/fileobject.h
+++ b/Include/fileobject.h
@@ -68,6 +68,17 @@
 */
 int _PyFile_SanitizeMode(char *mode);
 
+#if defined _MSC_VER && _MSC_VER >= 1400
+/* A routine to check if a file descriptor is valid on Windows.  Returns 0
+ * and sets errno to EBADF if it isn't.  This is to avoid Assertions
+ * from various functions in the Windows CRT beginning with
+ * Visual Studio 2005
+ */
+int _PyVerify_fd(int fd);
+#else
+#define _PyVerify_fd(A) (1) /* dummy */
+#endif
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/Modules/_fileio.c b/Modules/_fileio.c
index 2fc6de8..409abf6 100644
--- a/Modules/_fileio.c
+++ b/Modules/_fileio.c
@@ -127,7 +127,7 @@
 {
 #if defined(HAVE_FSTAT)
 	struct stat buf;
-	if (fstat(fd, &buf) < 0 && errno == EBADF) {
+	if (!_PyVerify_fd(fd) || (fstat(fd, &buf) < 0 && errno == EBADF)) {
 		PyObject *exc;
 		char *msg = strerror(EBADF);
 		exc = PyObject_CallFunction(PyExc_OSError, "(is)",
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index cda8135..4f27cd1 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -343,6 +343,109 @@
 #endif
 #endif
 
+#if defined _MSC_VER && _MSC_VER >= 1400
+/* Microsoft CRT in VS2005 and higher will verify that a filehandle is
+ * valid and throw an assertion if it isn't.
+ * Normally, an invalid fd is likely to be a C program error and therefore
+ * an assertion can be useful, but it does contradict the POSIX standard
+ * which for write(2) states:
+ *    "Otherwise, -1 shall be returned and errno set to indicate the error."
+ *    "[EBADF] The fildes argument is not a valid file descriptor open for
+ *     writing."
+ * Furthermore, python allows the user to enter any old integer
+ * as a fd and should merely raise a python exception on error.
+ * The Microsoft CRT doesn't provide an official way to check for the
+ * validity of a file descriptor, but we can emulate its internal behaviour
+ * by using the exported __pinfo data member and knowledge of the 
+ * internal structures involved.
+ * The structures below must be updated for each version of visual studio
+ * according to the file internal.h in the CRT source, until MS comes
+ * up with a less hacky way to do this.
+ * (all of this is to avoid globally modifying the CRT behaviour using
+ * _set_invalid_parameter_handler() and _CrtSetReportMode())
+ */
+#if _MSC_VER >= 1500 /* VS 2008 */
+typedef struct {
+        intptr_t osfhnd;
+        char osfile;
+        char pipech;
+        int lockinitflag;
+        CRITICAL_SECTION lock;
+#ifndef _SAFECRT_IMPL
+        char textmode : 7;
+        char unicode : 1;
+        char pipech2[2];
+        __int64 startpos;
+        BOOL utf8translations;
+        char dbcsBuffer;
+        BOOL dbcsBufferUsed;
+#endif  /* _SAFECRT_IMPL */
+    }   ioinfo;
+#elif _MSC_VER >= 1400  /* VS 2005 */
+typedef struct {
+        intptr_t osfhnd;
+        char osfile;
+        char pipech;
+        int lockinitflag;
+        CRITICAL_SECTION lock;
+#ifndef _SAFECRT_IMPL
+        char textmode : 7;
+        char unicode : 1;
+        char pipech2[2];
+        __int64 startpos;
+        BOOL utf8translations;
+#endif  /* _SAFECRT_IMPL */
+    }   ioinfo;
+#endif
+
+extern __declspec(dllimport) ioinfo * __pioinfo[];
+#define IOINFO_L2E 5
+#define IOINFO_ARRAY_ELTS   (1 << IOINFO_L2E)
+#define IOINFO_ARRAYS 64
+#define _NHANDLE_           (IOINFO_ARRAYS * IOINFO_ARRAY_ELTS)
+#define FOPEN 0x01
+#define _NO_CONSOLE_FILENO (intptr_t)-2
+
+/* This function emulates what the windows CRT does to validate file handles */
+int
+_PyVerify_fd(int fd)
+{
+	const int i1 = fd >> IOINFO_L2E;
+	const int i2 = fd & ((1 << IOINFO_L2E) - 1);
+
+	/* See that it isn't a special CLEAR fileno */
+	if (fd != _NO_CONSOLE_FILENO) {
+		/* Microsoft CRT would check that 0<=fd<_nhandle but we can't do that.  Instead
+		 * we check pointer validity and other info
+		 */
+		if (0 <= i1 && i1 < IOINFO_ARRAYS && __pioinfo[i1] != NULL) {
+			/* finally, check that the file is open */
+			if (__pioinfo[i1][i2].osfile & FOPEN)
+				return 1;
+		}
+	}
+	errno = EBADF;
+	return 0;
+}
+
+/* the special case of checking dup2.  The target fd must be in a sensible range */
+static int
+_PyVerify_fd_dup2(int fd1, int fd2)
+{
+	if (!_PyVerify_fd(fd1))
+		return 0;
+	if (fd2 == _NO_CONSOLE_FILENO)
+		return 0;
+	if ((unsigned)fd2 < _NHANDLE_)
+		return 1;
+	else
+		return 0;
+}
+#else
+/* dummy version. _PyVerify_fd() is already defined in fileobject.h */
+#define _PyVerify_fd_dup2(A, B) (1)
+#endif
+
 /* Return a dictionary corresponding to the POSIX environment table */
 #ifdef WITH_NEXT_FRAMEWORK
 /* On Darwin/MacOSX a shared library or framework has no access to
@@ -581,6 +684,8 @@
 	fd = PyObject_AsFileDescriptor(fdobj);
 	if (fd < 0)
 		return NULL;
+	if (!_PyVerify_fd(fd))
+		return posix_error();
 	Py_BEGIN_ALLOW_THREADS
 	res = (*func)(fd);
 	Py_END_ALLOW_THREADS
@@ -6188,6 +6293,8 @@
 	int fd, res;
 	if (!PyArg_ParseTuple(args, "i:close", &fd))
 		return NULL;
+	if (!_PyVerify_fd(fd))
+		return posix_error();
 	Py_BEGIN_ALLOW_THREADS
 	res = close(fd);
 	Py_END_ALLOW_THREADS
@@ -6210,7 +6317,8 @@
 		return NULL;
 	Py_BEGIN_ALLOW_THREADS
 	for (i = fd_from; i < fd_to; i++)
-		close(i);
+		if (_PyVerify_fd(i))
+			close(i);
 	Py_END_ALLOW_THREADS
 	Py_RETURN_NONE;
 }
@@ -6226,6 +6334,8 @@
 	int fd;
 	if (!PyArg_ParseTuple(args, "i:dup", &fd))
 		return NULL;
+	if (!_PyVerify_fd(fd))
+		return posix_error();
 	Py_BEGIN_ALLOW_THREADS
 	fd = dup(fd);
 	Py_END_ALLOW_THREADS
@@ -6245,6 +6355,8 @@
 	int fd, fd2, res;
 	if (!PyArg_ParseTuple(args, "ii:dup2", &fd, &fd2))
 		return NULL;
+	if (!_PyVerify_fd_dup2(fd, fd2))
+		return posix_error();
 	Py_BEGIN_ALLOW_THREADS
 	res = dup2(fd, fd2);
 	Py_END_ALLOW_THREADS
@@ -6289,6 +6401,8 @@
 	if (PyErr_Occurred())
 		return NULL;
 
+	if (!_PyVerify_fd(fd))
+		return posix_error();
 	Py_BEGIN_ALLOW_THREADS
 #if defined(MS_WIN64) || defined(MS_WINDOWS)
 	res = _lseeki64(fd, pos, how);
@@ -6325,6 +6439,8 @@
 	buffer = PyString_FromStringAndSize((char *)NULL, size);
 	if (buffer == NULL)
 		return NULL;
+	if (!_PyVerify_fd(fd))
+		return posix_error();
 	Py_BEGIN_ALLOW_THREADS
 	n = read(fd, PyString_AsString(buffer), size);
 	Py_END_ALLOW_THREADS
@@ -6351,6 +6467,8 @@
 
 	if (!PyArg_ParseTuple(args, "is*:write", &fd, &pbuf))
 		return NULL;
+	if (!_PyVerify_fd(fd))
+		return posix_error();
 	Py_BEGIN_ALLOW_THREADS
 	size = write(fd, pbuf.buf, (size_t)pbuf.len);
 	Py_END_ALLOW_THREADS
@@ -6377,6 +6495,8 @@
         /* on OpenVMS we must ensure that all bytes are written to the file */
         fsync(fd);
 #endif
+	if (!_PyVerify_fd(fd))
+		return posix_error();
 	Py_BEGIN_ALLOW_THREADS
 	res = FSTAT(fd, &st);
 	Py_END_ALLOW_THREADS
@@ -6419,6 +6539,8 @@
 		PyMem_FREE(mode);
 		return NULL;
 	}
+	if (!_PyVerify_fd(fd))
+		return posix_error();
 	Py_BEGIN_ALLOW_THREADS
 #if !defined(MS_WINDOWS) && defined(HAVE_FCNTL_H)
 	if (mode[0] == 'a') {
@@ -6458,6 +6580,8 @@
 	int fd;
 	if (!PyArg_ParseTuple(args, "i:isatty", &fd))
 		return NULL;
+	if (!_PyVerify_fd(fd))
+		return PyBool_FromLong(0);
 	return PyBool_FromLong(isatty(fd));
 }
 
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 99cfb2b..2f2a330 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1972,28 +1972,6 @@
     if (PyDict_SetItemString(bdict, # TYPE, PyExc_ ## TYPE)) \
         Py_FatalError("Module dictionary insertion problem.");
 
-#if defined _MSC_VER && _MSC_VER >= 1400 && defined(__STDC_SECURE_LIB__)
-/* crt variable checking in VisualStudio .NET 2005 */
-#include <crtdbg.h>
-
-static int	prevCrtReportMode;
-static _invalid_parameter_handler	prevCrtHandler;
-
-/* Invalid parameter handler.  Sets a ValueError exception */
-static void
-InvalidParameterHandler(
-    const wchar_t * expression,
-    const wchar_t * function,
-    const wchar_t * file,
-    unsigned int line,
-    uintptr_t pReserved)
-{
-    /* Do nothing, allow execution to continue.  Usually this
-     * means that the CRT will set errno to EINVAL
-     */
-}
-#endif
-
 
 PyMODINIT_FUNC
 _PyExc_Init(void)
@@ -2153,13 +2131,6 @@
     }
 
     Py_DECREF(bltinmod);
-
-#if defined _MSC_VER && _MSC_VER >= 1400 && defined(__STDC_SECURE_LIB__)
-    /* Set CRT argument error handler */
-    prevCrtHandler = _set_invalid_parameter_handler(InvalidParameterHandler);
-    /* turn off assertions in debug mode */
-    prevCrtReportMode = _CrtSetReportMode(_CRT_ASSERT, 0);
-#endif
 }
 
 void
@@ -2167,9 +2138,4 @@
 {
     Py_XDECREF(PyExc_MemoryErrorInst);
     PyExc_MemoryErrorInst = NULL;
-#if defined _MSC_VER && _MSC_VER >= 1400 && defined(__STDC_SECURE_LIB__)
-    /* reset CRT error handling */
-    _set_invalid_parameter_handler(prevCrtHandler);
-    _CrtSetReportMode(_CRT_ASSERT, prevCrtReportMode);
-#endif
 }