diff --git a/crates/horizon-client/src/lan/advancements.rs b/crates/horizon-client/src/lan/advancements.rs
index 0e0caf7ff..e0b8ad450 100644
--- a/crates/horizon-client/src/lan/advancements.rs
+++ b/crates/horizon-client/src/lan/advancements.rs
@@ -144,6 +144,13 @@ impl ServerAdvancements {
     ) -> Option<Vec<u8>> {
         let n = self.tree.list.len();
         let first = visible.len() != n;
+        // flushDirty does nothing unless it is the first packet or progress
+        // changed: visibility follows progress alone, and every grant and
+        // revoke is in `changed`. This skips walking the whole tree for
+        // every player every tick.
+        if !first && changed.is_empty() {
+            return None;
+        }
         let now = self
             .tree
             .visible(&self.kids, |i| progress.done(&self.tree.list[i]));