diff --git a/src/Makefile.am b/src/Makefile.am
index 19710652..765673b1 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -70,6 +70,7 @@ nghttpd_SOURCES = ${HELPER_OBJECTS} ${HELPER_HFILES} nghttpd.cc \
 	HttpServer.cc HttpServer.h
 
 h2load_SOURCES = util.cc util.h http2.cc http2.h h2load.cc h2load.h \
+	ssl.cc ssl.h \
 	h2load_session.h \
 	h2load_http2_session.cc h2load_http2_session.h
 
diff --git a/src/h2load.cc b/src/h2load.cc
index 2e930501..8f0413af 100644
--- a/src/h2load.cc
+++ b/src/h2load.cc
@@ -50,6 +50,7 @@
 #ifdef HAVE_SPDYLAY
 #include "h2load_spdy_session.h"
 #endif // HAVE_SPDYLAY
+#include "ssl.h"
 #include "http2.h"
 #include "util.h"
 
@@ -684,6 +685,8 @@ int main(int argc, char **argv)
   SSL_load_error_strings();
   SSL_library_init();
 
+  ssl::LibsslGlobalLock();
+
   http_parser_url u;
   memset(&u, 0, sizeof(u));
   auto uri = argv[optind];
diff --git a/src/ssl.cc b/src/ssl.cc
new file mode 100644
index 00000000..5dcc179c
--- /dev/null
+++ b/src/ssl.cc
@@ -0,0 +1,74 @@
+/*
+ * nghttp2 - HTTP/2.0 C Library
+ *
+ * Copyright (c) 2014 Tatsuhiro Tsujikawa
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#include "ssl.h"
+
+#include <cassert>
+#include <vector>
+#include <mutex>
+#include <iostream>
+
+#include <openssl/crypto.h>
+
+namespace nghttp2 {
+
+namespace ssl {
+
+namespace {
+std::vector<std::mutex> ssl_global_locks;
+} // namespace
+
+namespace {
+void ssl_locking_cb(int mode, int type, const char *file, int line)
+{
+  if(mode & CRYPTO_LOCK) {
+    ssl_global_locks[type].lock();
+  } else {
+    ssl_global_locks[type].unlock();
+  }
+}
+} // namespace
+
+LibsslGlobalLock::LibsslGlobalLock()
+{
+  if(!ssl_global_locks.empty()) {
+    std::cerr << "OpenSSL global lock has been already set" << std::endl;
+    assert(0);
+  }
+  ssl_global_locks = std::vector<std::mutex>(CRYPTO_num_locks());
+  // CRYPTO_set_id_callback(ssl_thread_id); OpenSSL manual says that
+  // if threadid_func is not specified using
+  // CRYPTO_THREADID_set_callback(), then default implementation is
+  // used. We use this default one.
+  CRYPTO_set_locking_callback(ssl_locking_cb);
+}
+
+LibsslGlobalLock::~LibsslGlobalLock()
+{
+  ssl_global_locks.clear();
+}
+
+} // namespace ssl
+
+} // namespace nghttp2
diff --git a/src/ssl.h b/src/ssl.h
new file mode 100644
index 00000000..fb3ae5aa
--- /dev/null
+++ b/src/ssl.h
@@ -0,0 +1,43 @@
+/*
+ * nghttp2 - HTTP/2.0 C Library
+ *
+ * Copyright (c) 2012 Tatsuhiro Tsujikawa
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#include "nghttp2_config.h"
+
+namespace nghttp2 {
+
+namespace ssl {
+
+// Acquire OpenSSL global lock to share SSL_CTX across multiple
+// threads. The constructor acquires lock and destructor unlocks.
+class LibsslGlobalLock {
+public:
+  LibsslGlobalLock();
+  ~LibsslGlobalLock();
+  LibsslGlobalLock(const LibsslGlobalLock&) = delete;
+  LibsslGlobalLock& operator=(const LibsslGlobalLock&) = delete;
+};
+
+} // namespace ssl
+
+} // namespace nghttp2