diff --git a/rag/raptor.py b/rag/raptor.py
index 99155e19d..d09ea5719 100644
--- a/rag/raptor.py
+++ b/rag/raptor.py
@@ -77,11 +77,11 @@ class RecursiveAbstractiveProcessing4TreeOrganizedRetrieval:
         return optimal_clusters
 
     async def __call__(self, chunks, random_state, callback=None):
-        layers = [(0, len(chunks))]
-        start, end = 0, len(chunks)
         if len(chunks) <= 1:
             return []
         chunks = [(s, a) for s, a in chunks if s and len(a) > 0]
+        layers = [(0, len(chunks))]
+        start, end = 0, len(chunks)
 
         async def summarize(ck_idx: list[int]):
             nonlocal chunks