diff --git a/ChangeLog b/ChangeLog
index 5fd0fddff2..e4fa3c2ecd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sat Jan  3 10:14:51 2015  SHIBATA Hiroshi  <shibata.hiroshi@gmail.com>
+
+	* ext/openssl/ossl.h: Make `SSL_SESSION_cmp` use `CRYPTO_memcmp`
+	  [fix GH-591] Patch by @PiPeep
+	* ext/openssl/ossl_ssl_session.c: ditto.
+
 Sat Jan  3 09:54:32 2015  SHIBATA Hiroshi  <shibata.hiroshi@gmail.com>
 
 	* ext/fiddle/lib/fiddle/cparser.rb: Support for Fiddle::CParser
diff --git a/ext/openssl/ossl.h b/ext/openssl/ossl.h
index c843c06f5c..fd7c8401f3 100644
--- a/ext/openssl/ossl.h
+++ b/ext/openssl/ossl.h
@@ -64,6 +64,7 @@ extern "C" {
 #include <openssl/rand.h>
 #include <openssl/conf.h>
 #include <openssl/conf_api.h>
+#include <openssl/crypto.h>
 #undef X509_NAME
 #undef PKCS7_SIGNER_INFO
 #if defined(HAVE_OPENSSL_ENGINE_H) && defined(HAVE_EVP_CIPHER_CTX_ENGINE)
diff --git a/ext/openssl/ossl_ssl_session.c b/ext/openssl/ossl_ssl_session.c
index 5318f1a525..2fd853f9ff 100644
--- a/ext/openssl/ossl_ssl_session.c
+++ b/ext/openssl/ossl_ssl_session.c
@@ -79,7 +79,7 @@ int SSL_SESSION_cmp(const SSL_SESSION *a,const SSL_SESSION *b)
     if (a->ssl_version != b->ssl_version ||
 	a->session_id_length != b->session_id_length)
 	return 1;
-    return memcmp(a->session_id,b-> session_id, a->session_id_length);
+    return CRYPTO_memcmp(a->session_id, b->session_id, a->session_id_length);
 }
 #endif