diff --git a/src/engine/gameManager/SimulationManager.java b/src/engine/gameManager/SimulationManager.java
index ff3b676d..33580a59 100644
--- a/src/engine/gameManager/SimulationManager.java
+++ b/src/engine/gameManager/SimulationManager.java
@@ -252,7 +252,7 @@ public enum SimulationManager {
                 continue;
             }
 
-            if (mine.isActive && (LocalDateTime.now().isAfter(closeTime) || LocalDateTime.now().isBefore(openTime))) {
+            if (mine.isActive && mine.lastClaimer != null && (LocalDateTime.now().isAfter(closeTime) || LocalDateTime.now().isBefore(openTime))) {
                 mineWindowClose(mine);
             }
         }