Index: Modules/_struct.c
===================================================================
--- Modules/_struct.c	(revision 69497)
+++ Modules/_struct.c	(working copy)
@@ -1785,7 +1785,7 @@
 	assert( buffer_len >= 0 );
 
 	/* Extract the offset from the first argument */
-	offset = PyLong_AsSsize_t(PyTuple_GET_ITEM(args, 1));
+	offset = PyNumber_AsSsize_t(PyTuple_GET_ITEM(args, 1), PyExc_IndexError);
 	if (offset == -1 && PyErr_Occurred())
 		return NULL;
 
Index: Lib/test/test_struct.py
===================================================================
--- Lib/test/test_struct.py	(revision 69497)
+++ Lib/test/test_struct.py	(working copy)
@@ -524,6 +524,10 @@
         self.assertRaises(struct.error, s.pack_into, small_buf, 0, test_string)
         self.assertRaises(struct.error, s.pack_into, small_buf, 2, test_string)
 
+        # Test bogus offset (issue 3694)
+        sb = small_buf
+        self.assertRaises(TypeError, struct.pack_into, b'1', sb, None)
+
     def test_pack_into_fn(self):
         test_string = b'Reykjavik rocks, eow!'
         writable_buf = array.array('b', b' '*100)