diff --git a/zed/src/sum_tree/cursor.rs b/zed/src/sum_tree/cursor.rs
index 440e99ba9025d3819b47d21982c5e8b1f510641b..4f6ec810554826970f7f71508005a71c4203a3e5 100644
--- a/zed/src/sum_tree/cursor.rs
+++ b/zed/src/sum_tree/cursor.rs
@@ -271,6 +271,7 @@ where
         }
 
         self.at_end = self.stack.is_empty();
+        debug_assert!(self.stack.is_empty() || self.stack.last().unwrap().tree.0.is_leaf());
     }
 
     pub fn descend_to_first_item<F>(&mut self, mut subtree: &'a SumTree<T>, filter_node: F)
@@ -656,6 +657,7 @@ where
         }
 
         self.at_end = self.stack.is_empty();
+        debug_assert!(self.stack.is_empty() || self.stack.last().unwrap().tree.0.is_leaf());
         if bias == SeekBias::Left {
             let mut end = self.seek_dimension.clone();
             if let Some(summary) = self.item_summary() {