diff --git a/macosx/BlocklistScheduler.m b/macosx/BlocklistScheduler.m
index 64f297439..9eeb4820e 100644
--- a/macosx/BlocklistScheduler.m
+++ b/macosx/BlocklistScheduler.m
@@ -50,6 +50,9 @@ BlocklistScheduler * fScheduler = nil;
 
 - (void) updateSchedule
 {
+    if ([BlocklistDownloader isRunning])
+        return;
+    
     [self cancelSchedule];
     
     if (![[NSUserDefaults standardUserDefaults] boolForKey: @"Blocklist"]