diff --git a/Code/Network/RKRequestQueue.m b/Code/Network/RKRequestQueue.m
index 3a8793c2..131b4604 100644
--- a/Code/Network/RKRequestQueue.m
+++ b/Code/Network/RKRequestQueue.m
@@ -382,7 +382,9 @@ static const NSTimeInterval kFlushDelay = 0.3;
 }
 
 - (BOOL)containsRequest:(RKRequest*)request {
-    return [_requests containsObject:request];
+    @synchronized(self) {
+        return [_requests containsObject:request];
+    }
 }
 
 - (void)cancelRequest:(RKRequest*)request loadNext:(BOOL)loadNext {