Cryptography_add_osrandom_engine should be safe to call multiple times

2 files changed, 8 insertions, 1 deletions

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;