diff -r 07331638ac85 Lib/sqlite3/test/regression.py
--- a/Lib/sqlite3/test/regression.py	Thu Dec 19 13:47:35 2013 +0100
+++ b/Lib/sqlite3/test/regression.py	Thu Dec 19 13:54:57 2013 +0100
@@ -330,6 +330,11 @@ class RegressionTests(unittest.TestCase)
             datetime.datetime(2012, 4, 4, 15, 6, 0, 123456),
         ])
 
+    def CheckInvalidIsolationLevelType(self):
+        # isolation level is a string, not an integer
+        self.assertRaises(TypeError,
+                          sqlite.connect, ":memory:", isolation_level=123)
+
 
 def suite():
     regression_suite = unittest.makeSuite(RegressionTests, "Check")
diff -r 07331638ac85 Modules/_sqlite/connection.c
--- a/Modules/_sqlite/connection.c	Thu Dec 19 13:47:35 2013 +0100
+++ b/Modules/_sqlite/connection.c	Thu Dec 19 13:54:57 2013 +0100
@@ -128,7 +128,10 @@ int pysqlite_connection_init(pysqlite_Co
         Py_INCREF(isolation_level);
     }
     self->isolation_level = NULL;
-    pysqlite_connection_set_isolation_level(self, isolation_level);
+    if (pysqlite_connection_set_isolation_level(self, isolation_level) < 0) {
+        Py_DECREF(isolation_level);
+        return -1;
+    }
     Py_DECREF(isolation_level);
 
     self->statement_cache = (pysqlite_Cache*)PyObject_CallFunction((PyObject*)&pysqlite_CacheType, "Oi", self, cached_statements);