diff --git a/src/openai/_compat.py b/src/openai/_compat.py
index 020ffeb2ca..778bca4d02 100644
--- a/src/openai/_compat.py
+++ b/src/openai/_compat.py
@@ -149,7 +149,7 @@ def model_dump(
             exclude_defaults=exclude_defaults,
             # warnings are not supported in Pydantic v1
             warnings=True if PYDANTIC_V1 else warnings,
-            by_alias=by_alias,
+            by_alias=bool(by_alias) if by_alias is not None else True,
         )
     return cast(
         "dict[str, Any]",