Index: Modules/_struct.c
===================================================================
--- Modules/_struct.c	(revision 72551)
+++ Modules/_struct.c	(working copy)
@@ -314,6 +314,9 @@
 			return res;
 		}
 #endif
+		v = get_pylong(v);
+		if (v == NULL)
+			return -1;
 		wrapped = PyNumber_And(v, pylong_ulong_mask);
 		if (wrapped == NULL)
 			return -1;
Index: Lib/test/test_struct.py
===================================================================
--- Lib/test/test_struct.py	(revision 72551)
+++ Lib/test/test_struct.py	(working copy)
@@ -101,6 +101,8 @@
         self.assertRaises(struct.error, struct.pack, 'i', 3, 3, 3)
         self.assertRaises(struct.error, struct.pack, 'i', 'foo')
         self.assertRaises(struct.error, struct.pack, 'P', 'foo')
+        self.assertRaises(struct.error, struct.pack, 'I', 'foobar')
+        self.assertRaises(struct.error, struct.pack, 'L', 'foobar')
         self.assertRaises(struct.error, struct.unpack, 'd', 'flap')
         s = struct.pack('ii', 1, 2)
         self.assertRaises(struct.error, struct.unpack, 'iii', s)