diff --git a/mechanize/_opener.py b/mechanize/_opener.py
index ad8412d..d8f3aec 100644
--- a/mechanize/_opener.py
+++ b/mechanize/_opener.py
@@ -412,31 +412,24 @@ def build_opener(self, *handlers):
 
 build_opener = OpenerFactory().build_opener
 
-_opener = None
-urlopen_lock = _threading.Lock()
+class _tls(_threading.local):
+	_opener = None
+
+_tls00 = _tls()
+
 def urlopen(url, data=None, timeout=_sockettimeout._GLOBAL_DEFAULT_TIMEOUT):
-    global _opener
-    if _opener is None:
-        urlopen_lock.acquire()
-        try:
-            if _opener is None:
-                _opener = build_opener()
-        finally:
-            urlopen_lock.release()
-    return _opener.open(url, data, timeout)
+    global _tls00
+    if _tls00._opener is None:
+        _tls00._opener = build_opener()
+    return _tls00._opener.open(url, data, timeout)
 
 def urlretrieve(url, filename=None, reporthook=None, data=None,
                 timeout=_sockettimeout._GLOBAL_DEFAULT_TIMEOUT):
-    global _opener
-    if _opener is None:
-        urlopen_lock.acquire()
-        try:
-            if _opener is None:
-                _opener = build_opener()
-        finally:
-            urlopen_lock.release()
-    return _opener.retrieve(url, filename, reporthook, data, timeout)
+    global _tls00
+    if _tls00._opener is None:
+        _tls00._opener = build_opener()
+    return _tls00._opener.retrieve(url, filename, reporthook, data, timeout)
 
 def install_opener(opener):
-    global _opener
-    _opener = opener
+    global _tls00
+    _tls00._opener = opener
diff --git a/mechanize/_urllib2_fork.py b/mechanize/_urllib2_fork.py
index d0cfe38..9bf5713 100644
--- a/mechanize/_urllib2_fork.py
+++ b/mechanize/_urllib2_fork.py
@@ -110,16 +110,22 @@ def splithost(url):
 # used in User-Agent header sent
 __version__ = sys.version[:3]
 
-_opener = None
+import threading
+
+class _tls(threading.local):
+	_opener = None
+
+_tls00 = _tls()
+
 def urlopen(url, data=None, timeout=_sockettimeout._GLOBAL_DEFAULT_TIMEOUT):
-    global _opener
-    if _opener is None:
-        _opener = build_opener()
-    return _opener.open(url, data, timeout)
+    global _tls00
+    if _tls00._opener is None:
+        _tls00._opener = build_opener()
+    return _tls00._opener.open(url, data, timeout)
 
 def install_opener(opener):
-    global _opener
-    _opener = opener
+    global _tls00
+    _tls00._opener = opener
 
 # copied from cookielib.py
 _cut_port_re = re.compile(r":\d+$")