diff --git a/PyCriCodecs/usm.py b/PyCriCodecs/usm.py
index a077f78..040ce75 100644
--- a/PyCriCodecs/usm.py
+++ b/PyCriCodecs/usm.py
@@ -923,8 +923,7 @@ def build_header(self, SFV_list: list, SFA_chunks: list = False, SBT_chunks = No
                         0,
                         0
                     )
-                    chk += metadata
-                    chk.ljust(len(metadata) + padding, b"\x00")
+                    chk += metadata.ljust(len(metadata) + padding, b"\x00")
                     audio_metadata.append(chk)
                     chno += 1