Index: Objects/longobject.c
===================================================================
--- Objects/longobject.c	(revision 46475)
+++ Objects/longobject.c	(working copy)
@@ -170,6 +170,11 @@
 			"cannot convert float infinity to long");
 		return NULL;
 	}
+	if (Py_IS_NAN(dval)) {
+		PyErr_SetString(PyExc_ValueError,
+			"cannot convert float NaN to long");
+		return NULL;
+	}
 	if (dval < 0.0) {
 		neg = 1;
 		dval = -dval;