diff --git a/docling/datamodel/base_models.py b/docling/datamodel/base_models.py
index f76a066c..d9a829ed 100644
--- a/docling/datamodel/base_models.py
+++ b/docling/datamodel/base_models.py
@@ -301,7 +301,7 @@ class OpenAiChatMessage(BaseModel):
 class OpenAiResponseChoice(BaseModel):
     index: int
     message: OpenAiChatMessage
-    finish_reason: str
+    finish_reason: Optional[str]
 
 
 class OpenAiResponseUsage(BaseModel):