PyModule_AddObject steals a reference.  Fix all of the double calls to it by adding a Py_INCREF.  Also, some other assorted hacks which probably shouldn't be necessary but are at the moment.
diff --git a/src/crypto/pkey.c b/src/crypto/pkey.c
index 583a2a1..ab8363a 100644
--- a/src/crypto/pkey.c
+++ b/src/crypto/pkey.c
@@ -266,6 +266,9 @@
         return 0;
     }
 
+    /* PyModule_AddObject steals a reference.
+     */
+    Py_INCREF((PyObject *)&crypto_PKey_Type);
     if (PyModule_AddObject(module, "PKey", (PyObject *)&crypto_PKey_Type) != 0) {
         return 0;
     }