diff --git a/src/hpack/hpack.py b/src/hpack/hpack.py
index 7e33e77..20dce0a 100644
--- a/src/hpack/hpack.py
+++ b/src/hpack/hpack.py
@@ -313,7 +313,7 @@ def add(self, to_add: tuple[bytes, bytes], sensitive: bool, huffman: bool = Fals
         # can use the indexed literal.
         index, name, perfect = match
 
-        if perfect:
+        if perfect is not None:
             # Indexed representation.
             encoded = self._encode_indexed(index)
         else: