diff --git a/google/generativeai/types/generation_types.py b/google/generativeai/types/generation_types.py
index 45ca6b21b..5ad7ab73d 100644
--- a/google/generativeai/types/generation_types.py
+++ b/google/generativeai/types/generation_types.py
@@ -526,7 +526,7 @@ def text(self):
                 texts.extend([f"```{outcome_result}", part.code_execution_result.output, "```"])
                 continue
 
-            part_type = protos.Part.pb(part).whichOneof("data")
+            part_type = protos.Part.pb(part).whichOneOf("data")
             raise ValueError(f"Could not convert `part.{part_type}` to text.")
 
         return "\n".join(texts)