diff --git a/src/pocketmine/level/generator/GenerationManager.php b/src/pocketmine/level/generator/GenerationManager.php
index 2734461371..694d2b0205 100644
--- a/src/pocketmine/level/generator/GenerationManager.php
+++ b/src/pocketmine/level/generator/GenerationManager.php
@@ -275,7 +275,10 @@ class GenerationManager{
 				$this->shutdown = true;
 			}
 		}elseif(count($this->thread->getInternalQueue()) === 0){
-			$this->thread->wait(50000);
+			$this->thread->synchronized(function(){
+				$this->thread->wait(50000);
+			});
+
 		}
 	}