diff --git a/api/src/routers/development.py b/api/src/routers/development.py
index d78aa3c..dc21c96 100644
--- a/api/src/routers/development.py
+++ b/api/src/routers/development.py
@@ -225,8 +225,8 @@ async def create_captioned_speech(
 
                                 # Add any chunks that may be in the acumulator into the return word_timestamps
                                 if chunk_data.word_timestamps is not None:
-                                    chunk_data.word_timestamps = (
-                                        timestamp_acumulator + chunk_data.word_timestamps
+                                    chunk_data.word_timestamps = (timestamp_acumulator or []) + (chunk_data.word_timestamps or [])
+
                                     )
                                     timestamp_acumulator = []
                                 else: