diff --git a/optuna/study/_tell.py b/optuna/study/_tell.py
index 0e51d63e04..d66f3be2ea 100644
--- a/optuna/study/_tell.py
+++ b/optuna/study/_tell.py
@@ -59,15 +59,18 @@ def _check_state_and_values(
 
 
 def _check_values_are_feasible(study: Study, values: Sequence[float]) -> str | None:
+    float_cast = float
+    isnan = math.isnan
+
     for v in values:
         # TODO(Imamura): Construct error message taking into account all values and do not early
         # return `value` is assumed to be ignored on failure so we can set it to any value.
         try:
-            float(v)
+            float_cast(v)
         except (ValueError, TypeError):
             return f"The value {repr(v)} could not be cast to float"
 
-        if math.isnan(v):
+        if isnan(v):
             return f"The value {v} is not acceptable"
 
     if len(study.directions) != len(values):