diff --git a/client.py b/client.py
--- a/client.py
+++ b/client.py
@@ -36,7 +36,8 @@ while len(nodeStack)>0:
   assert jsonData["dataType"]=="hash"
   
   if localTree.store[i]!=binData:
-    if 2*i+3<len(localTree.store): # inner node
+    # ie. 0-6 nodes, 7-14 leaves. 2*6+2<15
+    if 2*i+2<len(localTree.store): # inner node
       nodeStack.append(2*i+2)
       nodeStack.append(2*i+1)
     else: blocksToTransfer.append(i-localTree.leafStart) # leaf