Use TLS for the PyThreadState pointer instead of a field on Connection; this allows a Connection to be used safely in multiple threads concurrently
diff --git a/src/ssl/connection.h b/src/ssl/connection.h
index dedb73e..13f42f0 100644
--- a/src/ssl/connection.h
+++ b/src/ssl/connection.h
@@ -42,7 +42,7 @@
     SSL                 *ssl;
     ssl_ContextObj      *context;
     PyObject            *socket;
-    PyThreadState       *tstate;
+    PyThreadState       *tstate; /* This field is no longer used. */
     PyObject            *app_data;
 } ssl_ConnectionObj;
 
diff --git a/src/ssl/ssl.c b/src/ssl/ssl.c
index 7f58771..1f8cbcc 100644
--- a/src/ssl/ssl.c
+++ b/src/ssl/ssl.c
@@ -32,6 +32,8 @@
 
 void **crypto_API;
 
+int _pyOpenSSL_tstate_key;
+
 /* Exceptions defined by the SSL submodule */
 PyObject *ssl_Error,                   /* Base class              */
          *ssl_ZeroReturnError,         /* Used with SSL_get_error */
@@ -201,6 +203,13 @@
     if (!init_ssl_connection(dict))
         goto error;
 
-error:
+#ifdef WITH_THREAD
+    /*
+     * Initialize this module's threading support structures.
+     */
+    _pyOpenSSL_tstate_key = PyThread_create_key();
+#endif
+
+  error:
     ;
 }
diff --git a/src/ssl/ssl.h b/src/ssl/ssl.h
index e8d3e93..9cf0186 100644
--- a/src/ssl/ssl.h
+++ b/src/ssl/ssl.h
@@ -14,6 +14,7 @@
 #define PyOpenSSL_SSL_H_
 
 #include <Python.h>
+#include <pythread.h>
 #include "context.h"
 #include "connection.h"
 #include "../util.h"
@@ -45,6 +46,10 @@
 
 #define ssl_API_pointers          2
 
+#ifdef WITH_THREAD
+extern int _pyOpenSSL_tstate_key;
+#endif /* WITH_THREAD */
+
 #ifdef SSL_MODULE
 
 extern ssl_Context_New_RETURN    ssl_Context_New    ssl_Context_New_PROTO;
diff --git a/src/util.h b/src/util.h
index 592660e..b95e75b 100644
--- a/src/util.h
+++ b/src/util.h
@@ -30,10 +30,21 @@
  * WHERE to save the thread state.
  */
 #ifdef WITH_THREAD
-#  define MY_BEGIN_ALLOW_THREADS(st)    \
-    { st = PyEval_SaveThread(); }
-#  define MY_END_ALLOW_THREADS(st)      \
-    { PyEval_RestoreThread(st); st = NULL; }
+
+/*
+ * Get the current Python threadstate and put it somewhere any code running
+ * in this thread can get it, if it needs to restore the threadstate to run
+ * some Python.
+ */
+#  define MY_BEGIN_ALLOW_THREADS(ignored)                               \
+    PyThread_set_key_value(_pyOpenSSL_tstate_key, PyEval_SaveThread());
+
+/*
+ * Get the previous Python threadstate and restore it.
+ */
+#  define MY_END_ALLOW_THREADS(ignored)                                 \
+    PyEval_RestoreThread(PyThread_get_key_value(_pyOpenSSL_tstate_key));
+
 #else
 #  define MY_BEGIN_ALLOW_THREADS(st)
 #  define MY_END_ALLOW_THREADS(st)      { st = NULL; }