diff --git a/Lib/test/test_multiprocessing.py b/Lib/test/test_multiprocessing.py
index 2daff7edfdb..d4ce4fa2fe8 100644
--- a/Lib/test/test_multiprocessing.py
+++ b/Lib/test/test_multiprocessing.py
@@ -61,6 +61,8 @@ else:
 HAVE_GETVALUE = not getattr(_multiprocessing,
                             'HAVE_BROKEN_SEM_GETVALUE', False)
 
+WIN32 = (sys.platform == "win32")
+
 #
 # Creates a wrapper for a function which records the time it takes to finish
 #
@@ -1682,6 +1684,18 @@ class _TestLogging(BaseTestCase):
         logger.setLevel(level=LOG_LEVEL)
 
 #
+# Test to verify handle verification, see issue 3321
+#
+
+class TestInvalidHandle(unittest.TestCase):
+
+    def test_invalid_handles(self):
+        if WIN32:
+            return
+        conn = _multiprocessing.Connection(44977608)
+        self.assertRaises(IOError, conn.poll)
+        self.assertRaises(IOError, _multiprocessing.Connection, -1)
+#
 # Functions used to create test cases from the base ones in this module
 #
 
@@ -1785,7 +1799,7 @@ class OtherTest(unittest.TestCase):
                           multiprocessing.connection.answer_challenge,
                           _FakeConnection(), b'abc')
 
-testcases_other = [OtherTest]
+testcases_other = [OtherTest, TestInvalidHandle]
 
 #
 #
diff --git a/Misc/NEWS b/Misc/NEWS
index 293ab4aa2e2..8ef9cefbeac 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -140,6 +140,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #3321: _multiprocessing.Connection() doesn't check handle; added checks
+  for *nix machines for negative handles and large int handles. Without this check
+  it is possible to segfault the interpreter.
+
 - Issue #4449: AssertionError in mp_benchmarks.py, caused by an underlying issue
   in sharedctypes.py.
 
diff --git a/Modules/_multiprocessing/connection.h b/Modules/_multiprocessing/connection.h
index 155b61b57ca..458d1d3cf30 100644
--- a/Modules/_multiprocessing/connection.h
+++ b/Modules/_multiprocessing/connection.h
@@ -354,7 +354,7 @@ connection_poll(ConnectionObject *self, PyObject *args)
 	}
 
 	Py_BEGIN_ALLOW_THREADS
-	res = conn_poll(self, timeout);
+	res = conn_poll(self, timeout, _save);
 	Py_END_ALLOW_THREADS
 
 	switch (res) {
diff --git a/Modules/_multiprocessing/socket_connection.c b/Modules/_multiprocessing/socket_connection.c
index e5d2d155d9f..ad4005b2e80 100644
--- a/Modules/_multiprocessing/socket_connection.c
+++ b/Modules/_multiprocessing/socket_connection.c
@@ -153,11 +153,23 @@ conn_recv_string(ConnectionObject *conn, char *buffer,
  */
 
 static int
-conn_poll(ConnectionObject *conn, double timeout)
+conn_poll(ConnectionObject *conn, double timeout, PyThreadState *_save)
 {
 	int res;
 	fd_set rfds;
 
+	/*
+	 * Verify the handle, issue 3321. Not required for windows.
+	 */ 
+	#ifndef MS_WINDOWS
+		if (((int)conn->handle) < 0 || ((int)conn->handle) >= FD_SETSIZE) {
+			Py_BLOCK_THREADS
+			PyErr_SetString(PyExc_IOError, "handle out of range in select()");
+			Py_UNBLOCK_THREADS
+			return MP_EXCEPTION_HAS_BEEN_SET;
+		}
+	#endif
+
 	FD_ZERO(&rfds);
 	FD_SET((SOCKET)conn->handle, &rfds);