diff --git a/AFNetworking/AFNetworkActivityIndicatorManager.m b/AFNetworking/AFNetworkActivityIndicatorManager.m
index 5672773..ec3eabc 100644
--- a/AFNetworking/AFNetworkActivityIndicatorManager.m
+++ b/AFNetworking/AFNetworkActivityIndicatorManager.m
@@ -118,6 +118,9 @@ static NSTimeInterval const kAFNetworkActivityIndicatorInvisibilityDelay = 0.17;
 }
 
 - (void)decrementActivityCount {
+    if (_activityCount == 0) {
+        return;
+    }
     [self willChangeValueForKey:@"activityCount"];
 	@synchronized(self) {
 		_activityCount--;