diff --git a/hwe/sammo/ServerTool.php b/hwe/sammo/ServerTool.php
index 3188b3f7..1df104d0 100644
--- a/hwe/sammo/ServerTool.php
+++ b/hwe/sammo/ServerTool.php
@@ -14,12 +14,23 @@ final class ServerTool
         if ((120 % $turnterm) != 0) {
             return 'invalid minute';
         }
-
+        
 
         $db = DB::db();
         $gameStor = KVStorage::getStorage($db, 'game_env');
         $admin = $gameStor->getValues(['turntime', 'turnterm', 'year', 'startyear', 'month', 'isunited']);
 
+        $oldunit = $admin['turnterm'] * 60;
+        $unit = $turnterm * 60;
+
+        if($unit == $oldunit){
+            return null;
+        }
+
+        if($oldunit < 0 || $unit < 0){
+            return 'variable_turnterm';
+        }
+
         $reqGameLock = $admin['isunited'] != 2 && !$ignoreLock;
 
         $locked = false;
@@ -40,15 +51,6 @@ final class ServerTool
             $locked = tryLock();
         }
 
-        $oldunit = $admin['turnterm'] * 60;
-        $unit = $turnterm * 60;
-
-        if($unit == $oldunit){
-            if($locked){
-                unlock();
-            }
-            return null;
-        }
 
         $unitDiff = $unit / $oldunit;