diff --git a/src/SlotDbClient.php b/src/SlotDbClient.php
index e24e40e..87d6c8e 100644
--- a/src/SlotDbClient.php
+++ b/src/SlotDbClient.php
@@ -50,6 +50,9 @@ class SlotDbClient
     public function querySlot(string $slotId): array
     {
         $res = $this->get("/slot/{$slotId}");
+        if ($res->getStatusCode() == 404) {
+            throw new \RuntimeException("Invalid slot id");
+        }
         $data = json_decode($res->getBody(), true);
         return $data;
     }
@@ -119,6 +122,9 @@ class SlotDbClient
     public function queryGroup(string $groupId): array
     {
         $res = $this->get("/group/{$groupId}");
+        if ($res->getStatusCode() == 404) {
+            throw new \RuntimeException("Invalid group id");
+        }
         $data = json_decode($res->getBody(), true);
         return $data;
     }