From 7f25030b5308eef4cb8a276f1e91ca1647a80d8e Mon Sep 17 00:00:00 2001
From: Paul Kehrer <paul.l.kehrer@gmail.com>
Date: Thu, 20 Feb 2014 21:21:47 -0600
Subject: Cryptography_add_osrandom_engine should be safe to call multiple
 times

---
 cryptography/hazmat/bindings/openssl/binding.py         | 2 +-
 cryptography/hazmat/bindings/openssl/osrandom_engine.py | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/cryptography/hazmat/bindings/openssl/binding.py b/cryptography/hazmat/bindings/openssl/binding.py
index 714ecc07..0469a1ea 100644
--- a/cryptography/hazmat/bindings/openssl/binding.py
+++ b/cryptography/hazmat/bindings/openssl/binding.py
@@ -98,7 +98,7 @@ class Binding(object):
                                      _OSX_PRE_INCLUDE, _OSX_POST_INCLUDE,
                                      libraries)
         res = cls.lib.Cryptography_add_osrandom_engine()
-        assert res == 1
+        assert res != 0
 
     @classmethod
     def is_available(cls):
diff --git a/cryptography/hazmat/bindings/openssl/osrandom_engine.py b/cryptography/hazmat/bindings/openssl/osrandom_engine.py
index 23f2e17a..bbb3d642 100644
--- a/cryptography/hazmat/bindings/openssl/osrandom_engine.py
+++ b/cryptography/hazmat/bindings/openssl/osrandom_engine.py
@@ -175,6 +175,13 @@ static RAND_METHOD osrandom_rand = {
 };
 
 int Cryptography_add_osrandom_engine(void) {
+    ENGINE *engine = ENGINE_by_id(Cryptography_osrandom_engine_id);
+    if (engine != NULL) {
+        // The engine has already been added,
+        ENGINE_free(engine);
+        return 2;
+    }
+
     ENGINE *e = ENGINE_new();
     if (e == NULL) {
         return 0;
-- 
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