diff --git a/models/Generation.py b/models/Generation.py
index ea4500b..784d513 100644
--- a/models/Generation.py
+++ b/models/Generation.py
@@ -41,7 +41,7 @@ class Generation(BaseModel):
 
     @computed_field
     def cost(self) -> float:
-        if self.status == GenerationStatus.DONE:
+        if self.status == GenerationStatus.DONE and self.input_token_usage and self.output_token_usage:
             cost_input = self.input_token_usage * 0.000002
             cost_output = self.output_token_usage * 0.00012
             return round(cost_input + cost_output, 3)