diff --git a/src/pocketmine/scheduler/ServerScheduler.php b/src/pocketmine/scheduler/ServerScheduler.php
index 3f07099a7..c4a3b4854 100644
--- a/src/pocketmine/scheduler/ServerScheduler.php
+++ b/src/pocketmine/scheduler/ServerScheduler.php
@@ -172,7 +172,7 @@ class ServerScheduler{
 			$delay = -1;
 		}
 
-		if($period < -1){
+		if($period <= -1){
 			$period = -1;
 		}elseif($period < 1){
 			$period = 1;