diff --git a/subxt/src/backend/unstable/mod.rs b/subxt/src/backend/unstable/mod.rs
index 7dfe25bc6d..07177bb9d1 100644
--- a/subxt/src/backend/unstable/mod.rs
+++ b/subxt/src/backend/unstable/mod.rs
@@ -576,6 +576,10 @@ impl<T: Config + Send + Sync + 'static> Backend<T> for UnstableBackend<T> {
                         }
                         SeenBlock::Finalized(block_refs) => {
                             for block_ref in block_refs {
+                                if !seen_blocks.contains_key(&block_ref.hash()) {
+                                    panic!("Finalized before new Finalized {:#?}\n MEMLOG{:#?}\n SeenBlocks{:#?} \n Other{:#?}", block_ref.hash(), mem_log, seen_blocks, seen_other);
+                                }
+
                                 let entry = seen_blocks.entry(block_ref.hash()).or_insert((
                                     SeenBlockMarker::Finalized,
                                     block_ref.clone(),