diff --git a/src/transformers/generation/utils.py b/src/transformers/generation/utils.py
index 5b75a2519..3abd604cd 100644
--- a/src/transformers/generation/utils.py
+++ b/src/transformers/generation/utils.py
@@ -1394,7 +1394,7 @@ class GenerationMixin:
             return model_kwargs
 
         past_length = 0
-        if "past_key_values" in model_kwargs:
+        if model_kwargs.get("past_key_values") is not None:
             if isinstance(model_kwargs["past_key_values"], Cache):
                 past_length = model_kwargs["past_key_values"].get_seq_length()
             else: