diff --git a/crates/catalog/src/dates.rs b/crates/catalog/src/dates.rs
index d180d013d..4d16c2f4d 100644
--- a/crates/catalog/src/dates.rs
+++ b/crates/catalog/src/dates.rs
@@ -49,7 +49,9 @@ pub fn shift_iso(iso: &str, secs: i64) -> Option<String> {
     if !(first..=last).contains(&t) {
         return None;
     }
-    let tail = iso.trim().get(19..).unwrap_or("");
+    let iso = iso.trim();
+    // the seconds are optional (`10:00+02:00`): without them the tail starts right after the minutes
+    let tail = iso.get(if iso.get(16..17) == Some(":") { 19 } else { 16 }..).unwrap_or("");
     Some(format!("{}{tail}", civil(t)))
 }
 
@@ -222,6 +224,15 @@ mod tests {
         assert_eq!(normalize_iso("2026-02-30"), None);
     }
 
+    #[test]
+    fn shift_keeps_the_zone_of_a_time_without_seconds() {
+        assert_eq!(shift_iso("2026-01-01T10:00+02:00", 3600).as_deref(), Some("2026-01-01T11:00:00+02:00"));
+        assert_eq!(shift_iso("2026-01-01T10:00Z", 60).as_deref(), Some("2026-01-01T10:01:00Z"));
+        assert_eq!(shift_iso("2026-01-01T10:00", 3600).as_deref(), Some("2026-01-01T11:00:00"));
+        assert_eq!(shift_iso("2026-01-01T10:00:00.5-05:00", 3600).as_deref(), Some("2026-01-01T11:00:00.5-05:00"));
+        assert_eq!(iso_seconds("2026-01-01T10:00+02:00"), iso_seconds("2026-01-01T10:00"));
+    }
+
     #[test]
     fn runs_by_day_month_year_keep_stacks_together() {
         let mut c = Catalog::new();
diff --git a/crates/catalog/src/stacks.rs b/crates/catalog/src/stacks.rs
index a713b7736..eb7e89ef4 100644
--- a/crates/catalog/src/stacks.rs
+++ b/crates/catalog/src/stacks.rs
@@ -294,7 +294,8 @@ pub fn iso_seconds(s: &str) -> Option<i64> {
     if !(1..=12).contains(&m) || !(1..=31).contains(&d) {
         return None;
     }
-    let (hh, mm, ss) = if s.len() >= 16 { (num(11, 13)?, num(14, 16)?, num(17, 19).unwrap_or(0)) } else { (0, 0, 0) };
+    let (hh, mm, ss) =
+        if s.len() >= 16 { (num(11, 13)?, num(14, 16)?, if s.get(16..17) == Some(":") { num(17, 19).unwrap_or(0) } else { 0 }) } else { (0, 0, 0) };
     // days from civil (proleptic Gregorian)
     let y2 = if m <= 2 { y - 1 } else { y };
     let era = y2.div_euclid(400);