diff -r 1dc925ee441a Lib/test/test_heapq.py
--- a/Lib/test/test_heapq.py	Sat Sep 14 21:16:39 2013 +0200
+++ b/Lib/test/test_heapq.py	Sun Sep 15 00:12:42 2013 +0300
@@ -158,6 +158,15 @@
         self.assertEqual(sorted(chain(*inputs)), list(self.module.merge(*inputs)))
         self.assertEqual(list(self.module.merge()), [])
 
+    def test_merge_doesnt_suppress_index_error(self):
+        # Issue 19018: Heapq.merge suppresses IndexError from user generator
+        def iterable():
+            lst = range(10)
+            for i in xrange(20):
+                yield lst[i] # IndexError when i > 10
+        with self.assertRaises(IndexError):
+            list(self.module.merge(iterable(), iterable()))
+
     def test_merge_stability(self):
         class Int(int):
             pass