diff --git a/codex-rs/core/src/codex/timer_runtime.rs b/codex-rs/core/src/codex/timer_runtime.rs
index 0a1686751e..adac1929c1 100644
--- a/codex-rs/core/src/codex/timer_runtime.rs
+++ b/codex-rs/core/src/codex/timer_runtime.rs
@@ -204,6 +204,7 @@ impl Session {
             timer,
             context,
             deleted_one_shot_timer,
+            ..
         }) = self.claim_next_timer_for_delivery().await
         else {
             return false;
@@ -531,7 +532,7 @@ impl Session {
                     "failed to claim timer {} in sqlite: {err}",
                     claimed.timer.id
                 );
-                return true;
+                return false;
             }
         };
         let thread_id = self.thread_id_string();
@@ -548,7 +549,12 @@ impl Session {
                 return false;
             };
             state_db
-                .claim_recurring_thread_timer(&thread_id, &claimed.timer.id, &params)
+                .claim_recurring_thread_timer(
+                    &thread_id,
+                    &claimed.timer.id,
+                    claimed.previous_last_run_at,
+                    &params,
+                )
                 .await
         };
         match result {
diff --git a/codex-rs/core/src/timers.rs b/codex-rs/core/src/timers.rs
index 98f4ecc0da..cc7e59903b 100644
--- a/codex-rs/core/src/timers.rs
+++ b/codex-rs/core/src/timers.rs
@@ -80,6 +80,7 @@ pub(crate) struct ClaimedTimer {
     pub(crate) timer: ThreadTimer,
     pub(crate) context: TimerInvocationContext,
     pub(crate) deleted_one_shot_timer: bool,
+    pub(crate) previous_last_run_at: Option<i64>,
 }
 
 #[derive(Debug)]
@@ -397,12 +398,17 @@ impl TimersState {
         } = runtime;
         let is_recurring = timer.trigger.is_recurring();
         let deleted_one_shot_timer = !is_recurring;
+        let previous_last_run_at = timer.last_run_at;
         if deleted_one_shot_timer {
             if let Some(cancel) = timer_cancel.as_ref() {
                 cancel.cancel();
             }
         } else {
-            timer.last_run_at = Some(now.timestamp());
+            timer.last_run_at = Some(
+                previous_last_run_at
+                    .map(|previous| now.timestamp().max(previous.saturating_add(1)))
+                    .unwrap_or_else(|| now.timestamp()),
+            );
             let pending_run = timer.trigger.is_idle_recurring();
             self.timers.insert(
                 timer.id.clone(),
@@ -425,6 +431,7 @@ impl TimersState {
                 queued_at: now.timestamp(),
             },
             deleted_one_shot_timer,
+            previous_last_run_at,
         })
     }
 }
diff --git a/codex-rs/state/src/runtime/timers.rs b/codex-rs/state/src/runtime/timers.rs
index ea9cf00a74..c89ecc597b 100644
--- a/codex-rs/state/src/runtime/timers.rs
+++ b/codex-rs/state/src/runtime/timers.rs
@@ -158,6 +158,7 @@ WHERE thread_id = ?
         &self,
         thread_id: &str,
         id: &str,
+        expected_last_run_at: Option<i64>,
         params: &ThreadTimerUpdateParams,
     ) -> anyhow::Result<bool> {
         let result = sqlx::query(
@@ -174,6 +175,10 @@ SET trigger_json = ?,
 WHERE thread_id = ?
   AND id = ?
   AND pending_run = 1
+  AND (
+    (last_run_at IS NULL AND ? IS NULL)
+    OR last_run_at = ?
+  )
             "#,
         )
         .bind(params.trigger_json.as_str())
@@ -186,6 +191,8 @@ WHERE thread_id = ?
         .bind(i64::from(params.pending_run))
         .bind(thread_id)
         .bind(id)
+        .bind(expected_last_run_at)
+        .bind(expected_last_run_at)
         .execute(self.pool.as_ref())
         .await?;
         Ok(result.rows_affected() > 0)
@@ -374,13 +381,13 @@ ORDER BY name
 
         assert!(
             runtime
-                .claim_recurring_thread_timer("thread-1", "timer-1", &update)
+                .claim_recurring_thread_timer("thread-1", "timer-1", None, &update)
                 .await
                 .expect("claim recurring timer")
         );
         assert!(
             !runtime
-                .claim_recurring_thread_timer("thread-1", "timer-1", &update)
+                .claim_recurring_thread_timer("thread-1", "timer-1", None, &update)
                 .await
                 .expect("claim recurring timer again")
         );
@@ -397,4 +404,46 @@ ORDER BY name
         assert_eq!(timers[0].last_run_at, Some(110));
         assert!(!timers[0].pending_run);
     }
+
+    #[tokio::test]
+    async fn recurring_idle_claim_rejects_stale_last_run_at_even_when_pending_stays_true() {
+        let runtime = test_runtime().await;
+        let mut params = timer_params("timer-1", "thread-1");
+        params.pending_run = true;
+        params.last_run_at = Some(100);
+        runtime
+            .create_thread_timer(&params)
+            .await
+            .expect("create pending timer");
+        let update = ThreadTimerUpdateParams {
+            trigger_json: params.trigger_json.clone(),
+            content: params.content.clone(),
+            instructions: params.instructions.clone(),
+            meta_json: params.meta_json.clone(),
+            delivery: params.delivery.clone(),
+            next_run_at: Some(120),
+            last_run_at: Some(110),
+            pending_run: true,
+        };
+
+        assert!(
+            runtime
+                .claim_recurring_thread_timer("thread-1", "timer-1", Some(100), &update)
+                .await
+                .expect("claim recurring idle timer")
+        );
+        assert!(
+            !runtime
+                .claim_recurring_thread_timer("thread-1", "timer-1", Some(100), &update)
+                .await
+                .expect("claim recurring idle timer again")
+        );
+        let timers = runtime
+            .list_thread_timers("thread-1")
+            .await
+            .expect("list timers");
+        assert_eq!(timers.len(), 1);
+        assert_eq!(timers[0].last_run_at, Some(110));
+        assert!(timers[0].pending_run);
+    }
 }