diff --git a/beets/autotag/mb.py b/beets/autotag/mb.py
index a7553b1b1..30a8d07d2 100644
--- a/beets/autotag/mb.py
+++ b/beets/autotag/mb.py
@@ -20,10 +20,12 @@ syntax, and other uninteresting parts of using musicbrainz2. The
 principal interface is the function `match_album`.
 """
 
+from __future__ import with_statement # for Python 2.5
 import re
 import time
 import datetime
 import musicbrainz2.webservice as mbws
+from threading import Lock
 
 class ServerBusyError(Exception): pass
 
@@ -34,6 +36,7 @@ class ServerBusyError(Exception): pass
 MAX_QUERY_RETRY = 8
 QUERY_WAIT_TIME = 1.0
 last_query_time = 0.0
+mb_lock = Lock()
 def _query_wrap(fun, *args, **kwargs):
     """Wait until at least `QUERY_WAIT_TIME` seconds have passed since
     the last invocation of this function. Then call
@@ -41,25 +44,26 @@ def _query_wrap(fun, *args, **kwargs):
     then try again. Tries up to `MAX_QUERY_RETRY` times before
     giving up.
     """
-    global last_query_time
-    for i in range(MAX_QUERY_RETRY):
-        since_last_query = time.time() - last_query_time
-        if since_last_query < QUERY_WAIT_TIME:
-            time.sleep(QUERY_WAIT_TIME - since_last_query)
-        last_query_time = time.time()
-        try:
-            # Try the function.
-            res = fun(*args, **kwargs)
-        except mbws.WebServiceError, e:
-            # Server busy. Retry.
-            if 'Error 503' not in str(e.reason):
-                # This is not the error we're looking for.
-                raise
-        else:
-            # Success. Return the result.
-            return res
-    # Gave up.
-    raise ServerBusyError()
+    with mb_lock:
+        global last_query_time
+        for i in range(MAX_QUERY_RETRY):
+            since_last_query = time.time() - last_query_time
+            if since_last_query < QUERY_WAIT_TIME:
+                time.sleep(QUERY_WAIT_TIME - since_last_query)
+            last_query_time = time.time()
+            try:
+                # Try the function.
+                res = fun(*args, **kwargs)
+            except mbws.WebServiceError, e:
+                # Server busy. Retry.
+                if 'Error 503' not in str(e.reason):
+                    # This is not the error we're looking for.
+                    raise
+            else:
+                # Success. Return the result.
+                return res
+        # Gave up.
+        raise ServerBusyError()
     # FIXME exponential backoff?
 
 def _lucene_escape(text):