diff --git a/pageserver/src/tenant.rs b/pageserver/src/tenant.rs
index a98a32de35..f83c7021e3 100644
--- a/pageserver/src/tenant.rs
+++ b/pageserver/src/tenant.rs
@@ -7470,7 +7470,10 @@ mod tests {
             // Update GC info
             let mut guard = tline.gc_info.write().unwrap();
             *guard = GcInfo {
-                retain_lsns: vec![Lsn(0x10), Lsn(0x20)],
+                retain_lsns: vec![
+                    (Lsn(0x10), tline.timeline_id),
+                    (Lsn(0x20), tline.timeline_id),
+                ],
                 cutoffs: GcCutoffs {
                     time: Lsn(0x30),
                     space: Lsn(0x30),
diff --git a/pageserver/src/tenant/timeline/compaction.rs b/pageserver/src/tenant/timeline/compaction.rs
index fb8c125b60..d0a74e3924 100644
--- a/pageserver/src/tenant/timeline/compaction.rs
+++ b/pageserver/src/tenant/timeline/compaction.rs
@@ -1254,7 +1254,7 @@ impl Timeline {
             let gc_info = self.gc_info.read().unwrap();
             let mut retain_lsns_below_horizon = Vec::new();
             let gc_cutoff = gc_info.cutoffs.select_min();
-            for lsn in &gc_info.retain_lsns {
+            for (lsn, _timeline_id) in &gc_info.retain_lsns {
                 if lsn < &gc_cutoff {
                     retain_lsns_below_horizon.push(*lsn);
                 }