diff --git a/electrumx/lib/merkle.py b/electrumx/lib/merkle.py
index 65c4089..f9bd505 100644
--- a/electrumx/lib/merkle.py
+++ b/electrumx/lib/merkle.py
@@ -187,24 +187,20 @@ class MerkleCache(object):
         # Retain the value of depth_higher; in practice this is fine
         start = self._leaf_start(self.length)
         hashes = self.source.hashes(start, length - start)
-        self.level[start >> self.depth_higher] = self._level(hashes)
+        self.level[start >> self.depth_higher:] = self._level(hashes)
         self.length = length
 
     def _level_for(self, length):
         '''Return a (level_length, final_hash) pair for a truncation
-        of the hashes to the given length.  Length may be an extension,
-        in which case extra hashes are requested from the source.'''
-        if length > self.length:
-            hashes = self.source.hashes(self.length, length - self.length)
-            return self.level + self._level(hashes)
-        if length < self.length:
-            level = self.level[:length >> self.depth_higher]
-            leaf_start = self._leaf_start(length)
-            count = min(self._segment_length(), length - leaf_start)
-            hashes = self.source.hashes(leaf_start, count)
-            level += self._level(hashes)
-            return level
-        return self.level
+        of the hashes to the given length.'''
+        if length == self.length:
+            return self.level
+        level = self.level[:length >> self.depth_higher]
+        leaf_start = self._leaf_start(length)
+        count = min(self._segment_length(), length - leaf_start)
+        hashes = self.source.hashes(leaf_start, count)
+        level += self._level(hashes)
+        return level
 
     def branch_and_root(self, length, index):
         '''Return a merkle branch and root.  Length is the number of
diff --git a/tests/lib/test_merkle.py b/tests/lib/test_merkle.py
index c860020..e5859a2 100644
--- a/tests/lib/test_merkle.py
+++ b/tests/lib/test_merkle.py
@@ -172,7 +172,7 @@ def test_merkle_cache():
                 assert root == root2
 
 
-def merkle_cache_extension():
+def test_merkle_cache_extension():
     source = Source(64)
     for length in range(14, 18):
         for cp_length in range(30, 36):
@@ -201,6 +201,7 @@ def test_markle_cache_bad():
     with pytest.raises(ValueError):
         cache.branch_and_root(3, 3)
 
+
 def test_bad_extension():
     length = 5
     source = Source(length)