diff --git a/codewiki/src/be/llm_services.py b/codewiki/src/be/llm_services.py
index 38fca92b..034d0a66 100644
--- a/codewiki/src/be/llm_services.py
+++ b/codewiki/src/be/llm_services.py
@@ -13,7 +13,7 @@
 
 from openai.types import chat
 
-from pydantic_ai.exceptions import ModelHTTPError
+from pydantic_ai.exceptions import ModelHTTPError, UnexpectedModelBehavior
 from pydantic_ai.models.openai import OpenAIChatModel, OpenAIChatModelSettings
 from pydantic_ai.models.fallback import FallbackModel
 from pydantic_ai.providers.openai import OpenAIProvider
@@ -254,7 +254,11 @@ def create_fallback_models(config: Config) -> FallbackModel:
     """Create fallback models chain from configuration."""
     main = create_main_model(config)
     fallback = create_fallback_model(config)
-    return FallbackModel(main, fallback)
+    # Default fallback_on=(ModelHTTPError,) does NOT cover UnexpectedModelBehavior, which
+    # is what pydantic-ai raises for a 200 response with a malformed/empty body (seen once
+    # against OpenRouter: choices/model/object all None). Without this, that failure mode
+    # skips the fallback model entirely and kills the module outright.
+    return FallbackModel(main, fallback, fallback_on=(ModelHTTPError, UnexpectedModelBehavior))
 
 
 def create_openai_client(config: Config) -> OpenAI: