diff --git a/django/dispatch/dispatcher.py b/django/dispatch/dispatcher.py
index 3b6b72d044..9beb309ac1 100644
--- a/django/dispatch/dispatcher.py
+++ b/django/dispatch/dispatcher.py
@@ -1,4 +1,5 @@
 import weakref
+import threading
 
 from django.dispatch import saferef
 
@@ -30,6 +31,7 @@ class Signal(object):
         if providing_args is None:
             providing_args = []
         self.providing_args = set(providing_args)
+        self.lock = threading.Lock()
 
     def connect(self, receiver, sender=None, weak=True, dispatch_uid=None):
         """
@@ -97,11 +99,15 @@ class Signal(object):
         if weak:
             receiver = saferef.safeRef(receiver, onDelete=self._remove_receiver)
 
-        for r_key, _ in self.receivers:
-            if r_key == lookup_key:
-                break
-        else:
-            self.receivers.append((lookup_key, receiver))
+        try:
+            self.lock.acquire()
+            for r_key, _ in self.receivers:
+                if r_key == lookup_key:
+                    break
+            else:
+                self.receivers.append((lookup_key, receiver))
+        finally:
+            self.lock.release()
 
     def disconnect(self, receiver=None, sender=None, weak=True, dispatch_uid=None):
         """
@@ -130,11 +136,15 @@ class Signal(object):
         else:
             lookup_key = (_make_id(receiver), _make_id(sender))
         
-        for index in xrange(len(self.receivers)):
-            (r_key, _) = self.receivers[index]
-            if r_key == lookup_key:
-                del self.receivers[index]
-                break
+        try:
+            self.lock.acquire()
+            for index in xrange(len(self.receivers)):
+                (r_key, _) = self.receivers[index]
+                if r_key == lookup_key:
+                    del self.receivers[index]
+                    break
+        finally:
+            self.lock.release()
 
     def send(self, sender, **named):
         """
@@ -227,14 +237,21 @@ class Signal(object):
         Remove dead receivers from connections.
         """
 
-        to_remove = []
-        for key, connected_receiver in self.receivers:
-            if connected_receiver == receiver:
-                to_remove.append(key)
-        for key in to_remove:
-            for idx, (r_key, _) in enumerate(self.receivers):
-                if r_key == key:
-                    del self.receivers[idx]
+        try:
+            self.lock.acquire()
+            to_remove = []
+            for key, connected_receiver in self.receivers:
+                if connected_receiver == receiver:
+                    to_remove.append(key)
+            for key in to_remove:
+                last_idx = len(self.receivers) - 1
+                # enumerate in reverse order so that indexes are valid even
+                # after we delete some items
+                for idx, (r_key, _) in enumerate(reversed(self.receivers)):
+                    if r_key == key:
+                        del self.receivers[last_idx-idx]
+        finally:
+            self.lock.release()
 
 
 def receiver(signal, **kwargs):