diff --git a/cmaes/_cma.py b/cmaes/_cma.py
index 88dbce5..5f43e1c 100644
--- a/cmaes/_cma.py
+++ b/cmaes/_cma.py
@@ -400,6 +400,10 @@ def tell(self, solutions: list[tuple[np.ndarray, float]]) -> None:
 
         # Learning rate adaptation: https://arxiv.org/abs/2304.03473
         if self._lr_adapt:
+            assert isinstance(old_mean, np.ndarray)
+            assert isinstance(old_sigma, (int, float))
+            assert isinstance(old_Sigma, np.ndarray)
+            assert isinstance(old_invsqrtC, np.ndarray)
             self._lr_adaptation(old_mean, old_sigma, old_Sigma, old_invsqrtC)
 
     def _lr_adaptation(