diff --git a/ax/modelbridge/generation_strategy.py b/ax/modelbridge/generation_strategy.py
index d8a70e4a5fc..ba70b64035d 100644
--- a/ax/modelbridge/generation_strategy.py
+++ b/ax/modelbridge/generation_strategy.py
@@ -386,7 +386,7 @@ def _validate_and_set_step_sequence(self, steps: List[GenerationStep]) -> None:
 
             # Set transition_to field for all but the last step, which remains
             # null.
-            if idx != len(self._steps):
+            if idx != len(self._steps) - 1:
                 for transition_criteria in step.transition_criteria:
                     if (
                         transition_criteria.criterion_class