diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6d581ccce..209c9cb11 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,9 +33,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `CartesiaSTTService` now inherits from `WebsocketSTTService`.
 
 - Package upgrades:
+
   - `openai` upgraded to support up to 2.x.x.
   - `openpipe` upgraded to support up to 5.x.x.
 
+- `SpeechmaticsSTTService` updated dependencies for `speechmatics-rt>=0.5.0`.
+
 ### Fixed
 
 - Fixed multiple pipeline task cancellation issues. `asyncio.CancelledError` is
@@ -59,6 +62,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   incorrectly 16-bit aligned audio frames, potentially leading to internal
   errors or static audio.
 
+- Fixed an issue in `SpeechmaticsSTTService` where `AdditionalVocabEntry` items
+  needed to have `sounds_like` for the session to start.
+
 ### Other
 
 - Added foundational example `47-sentry-metrics.py`, demonstrating how to use the
diff --git a/pyproject.toml b/pyproject.toml
index 0d94d0fa3..65546311c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -102,7 +102,7 @@ silero = [ "onnxruntime>=1.20.1,<2" ]
 simli = [ "simli-ai~=0.1.10"]
 soniox = [ "pipecat-ai[websockets-base]" ]
 soundfile = [ "soundfile~=0.13.0" ]
-speechmatics = [ "speechmatics-rt>=0.4.0" ]
+speechmatics = [ "speechmatics-rt>=0.5.0" ]
 strands = [ "strands-agents>=1.9.1,<2" ]
 tavus=[]
 together = []
diff --git a/src/pipecat/services/speechmatics/stt.py b/src/pipecat/services/speechmatics/stt.py
index 2c1db2a15..901edb0e8 100644
--- a/src/pipecat/services/speechmatics/stt.py
+++ b/src/pipecat/services/speechmatics/stt.py
@@ -620,7 +620,7 @@ class SpeechmaticsSTTService(STTService):
             transcription_config.additional_vocab = [
                 {
                     "content": e.content,
-                    "sounds_like": e.sounds_like,
+                    **({"sounds_like": e.sounds_like} if e.sounds_like else {}),
                 }
                 for e in self._params.additional_vocab
             ]