diff --git a/proxy/src/main/java/net/md_5/bungee/scheduler/BungeeScheduler.java b/proxy/src/main/java/net/md_5/bungee/scheduler/BungeeScheduler.java
index 1dc1cc66e6..fd0dabcf46 100644
--- a/proxy/src/main/java/net/md_5/bungee/scheduler/BungeeScheduler.java
+++ b/proxy/src/main/java/net/md_5/bungee/scheduler/BungeeScheduler.java
@@ -62,9 +62,12 @@ public void cancel(ScheduledTask task)
     public int cancel(Plugin plugin)
     {
         Set<ScheduledTask> toRemove = new HashSet<>();
-        for ( ScheduledTask task : tasksByPlugin.get( plugin ) )
+        synchronized ( lock )
         {
-            toRemove.add( task );
+            for ( ScheduledTask task : tasksByPlugin.get( plugin ) )
+            {
+                toRemove.add( task );
+            }
         }
         for ( ScheduledTask task : toRemove )
         {