diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index b70e4b43c..5283c2587 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -6,6 +6,8 @@ repos:
         args:
           - --safe
           - --quiet
+          - --target-version
+          - py38
         files: ^((supervisor|tests)/.+)?[^/]+\.py$
   - repo: https://gitlab.com/pycqa/flake8
     rev: 3.8.3
diff --git a/supervisor/addons/addon.py b/supervisor/addons/addon.py
index ea4426d56..c0a520d07 100644
--- a/supervisor/addons/addon.py
+++ b/supervisor/addons/addon.py
@@ -39,6 +39,7 @@ from ..const import (
     ATTR_VERSION,
     ATTR_WATCHDOG,
     DNS_SUFFIX,
+    AddonStartup,
     AddonState,
 )
 from ..coresys import CoreSys
@@ -185,7 +186,12 @@ class Addon(AddonModel):
     @watchdog.setter
     def watchdog(self, value: bool) -> None:
         """Set watchdog enable/disable."""
-        self.persist[ATTR_WATCHDOG] = value
+        if value and self.startup == AddonStartup.ONCE:
+            _LOGGER.warning(
+                "Ignoring watchdog for %s because startup type is 'once'", self.slug
+            )
+        else:
+            self.persist[ATTR_WATCHDOG] = value
 
     @property
     def uuid(self) -> str: