diff --git a/nanobot/cron/service.py b/nanobot/cron/service.py
index 267613012..165ce54d7 100644
--- a/nanobot/cron/service.py
+++ b/nanobot/cron/service.py
@@ -80,6 +80,7 @@ class CronService:
         self._store: CronStore | None = None
         self._timer_task: asyncio.Task | None = None
         self._running = False
+        self._timer_active = False
         self.max_sleep_ms = max_sleep_ms
 
     def _load_jobs(self) -> tuple[list[CronJob], int]:
@@ -171,7 +172,11 @@ class CronService:
     def _load_store(self) -> CronStore:
         """Load jobs from disk. Reloads automatically if file was modified externally.
         - Reload every time because it needs to merge operations on the jobs object from other instances.
+        - During _on_timer execution, return the existing store to prevent concurrent
+          _load_store calls (e.g. from list_jobs polling) from replacing it mid-execution.
         """
+        if self._timer_active and self._store:
+            return self._store
         jobs, version = self._load_jobs()
         self._store = CronStore(version=version, jobs=jobs)
         self._merge_action()
@@ -290,18 +295,23 @@ class CronService:
         """Handle timer tick - run due jobs."""
         self._load_store()
         if not self._store:
+            self._arm_timer()
             return
 
-        now = _now_ms()
-        due_jobs = [
-            j for j in self._store.jobs
-            if j.enabled and j.state.next_run_at_ms and now >= j.state.next_run_at_ms
-        ]
+        self._timer_active = True
+        try:
+            now = _now_ms()
+            due_jobs = [
+                j for j in self._store.jobs
+                if j.enabled and j.state.next_run_at_ms and now >= j.state.next_run_at_ms
+            ]
 
-        for job in due_jobs:
-            await self._execute_job(job)
+            for job in due_jobs:
+                await self._execute_job(job)
 
-        self._save_store()
+            self._save_store()
+        finally:
+            self._timer_active = False
         self._arm_timer()
 
     async def _execute_job(self, job: CronJob) -> None: