diff --git a/swh/icinga_plugins/base_check.py b/swh/icinga_plugins/base_check.py
--- a/swh/icinga_plugins/base_check.py
+++ b/swh/icinga_plugins/base_check.py
@@ -1,16 +1,21 @@
-# Copyright (C) 2019  The Software Heritage developers
+# Copyright (C) 2019-2022  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
+from typing import Dict
+
 
 class BaseCheck:
-    def __init__(self, obj):
-        self.warning_threshold = obj.get(
-            "warning_threshold", self.DEFAULT_WARNING_THRESHOLD
+    DEFAULT_WARNING_THRESHOLD = 60
+    DEFAULT_CRITICAL_THRESHOLD = 120
+
+    def __init__(self, obj: Dict[str, str]) -> None:
+        self.warning_threshold = float(
+            obj.get("warning_threshold", self.DEFAULT_WARNING_THRESHOLD)
         )
-        self.critical_threshold = obj.get(
-            "critical_threshold", self.DEFAULT_CRITICAL_THRESHOLD
+        self.critical_threshold = float(
+            obj.get("critical_threshold", self.DEFAULT_CRITICAL_THRESHOLD)
         )
 
     def get_status(self, value):