diff --git a/src/api2/admin/sync.rs b/src/api2/admin/sync.rs
index ff1e5ebf..bea52a0a 100644
--- a/src/api2/admin/sync.rs
+++ b/src/api2/admin/sync.rs
@@ -57,7 +57,8 @@ pub fn list_sync_jobs(
         job.next_run = (|| -> Option<i64> {
             let schedule = job.schedule.as_ref()?;
             let event = parse_calendar_event(&schedule).ok()?;
-            compute_next_event(&event, last, false).ok()
+            // ignore errors
+            compute_next_event(&event, last, false).unwrap_or_else(|_| None)
         })();
     }
 
diff --git a/src/bin/proxmox-backup-proxy.rs b/src/bin/proxmox-backup-proxy.rs
index dd081dfe..2b43c5ac 100644
--- a/src/bin/proxmox-backup-proxy.rs
+++ b/src/bin/proxmox-backup-proxy.rs
@@ -301,7 +301,8 @@ async fn schedule_datastore_garbage_collection() {
         };
 
         let next = match compute_next_event(&event, last, false) {
-            Ok(next) => next,
+            Ok(Some(next)) => next,
+            Ok(None) => continue,
             Err(err) => {
                 eprintln!("compute_next_event for '{}' failed - {}", event_str, err);
                 continue;
@@ -412,7 +413,8 @@ async fn schedule_datastore_prune() {
         };
 
         let next = match compute_next_event(&event, last, false) {
-            Ok(next) => next,
+            Ok(Some(next)) => next,
+            Ok(None) => continue,
             Err(err) => {
                 eprintln!("compute_next_event for '{}' failed - {}", event_str, err);
                 continue;
@@ -520,7 +522,8 @@ async fn schedule_datastore_sync_jobs() {
         };
 
         let next = match compute_next_event(&event, last, false) {
-            Ok(next) => next,
+            Ok(Some(next)) => next,
+            Ok(None) => continue,
             Err(err) => {
                 eprintln!("compute_next_event for '{}' failed - {}", event_str, err);
                 continue;
diff --git a/src/tools/systemd/time.rs b/src/tools/systemd/time.rs
index 8bb2a8f7..2e99e289 100644
--- a/src/tools/systemd/time.rs
+++ b/src/tools/systemd/time.rs
@@ -1,4 +1,4 @@
-use anyhow::{bail, Error};
+use anyhow::Error;
 use bitflags::bitflags;
 
 pub use super::parse_time::*;
@@ -155,7 +155,7 @@ pub fn compute_next_event(
     event: &CalendarEvent,
     last: i64,
     utc: bool,
-) -> Result<i64, Error> {
+) -> Result<Option<i64>, Error> {
 
     let last = last + 1; // at least one second later
 
@@ -166,8 +166,9 @@ pub fn compute_next_event(
     let mut count = 0;
 
     loop {
-        if count > 1000 { // should not happen
-            bail!("unable to compute next calendar event");
+        // cancel after 1000 loops
+        if count > 1000 {
+            return Ok(None);
         } else {
             count += 1;
         }
@@ -235,13 +236,15 @@ pub fn compute_next_event(
         }
 
         let next = t.into_epoch()?;
-        return Ok(next)
+        return Ok(Some(next))
     }
 }
 
 #[cfg(test)]
 mod test {
 
+    use anyhow::bail;
+
     use super::*;
     use proxmox::tools::time::*;
 
@@ -268,7 +271,7 @@ mod test {
             };
 
             match compute_next_event(&event, last, true) {
-                Ok(next) => {
+                Ok(Some(next)) => {
                     if next == expect {
                         println!("next {:?} => {}", event, next);
                     } else {
@@ -276,6 +279,7 @@ mod test {
                               event, gmtime(next), gmtime(expect));
                     }
                 }
+                Ok(None) => bail!("next {:?} failed to find a timestamp", event),
                 Err(err) => bail!("compute next for '{}' failed - {}", v, err),
             }