diff --git a/src/iterative_ensemble_smoother/esmda.py b/src/iterative_ensemble_smoother/esmda.py
index de8ef9eb..5357f0a8 100644
--- a/src/iterative_ensemble_smoother/esmda.py
+++ b/src/iterative_ensemble_smoother/esmda.py
@@ -159,7 +159,6 @@ def __init__(
             raise TypeError("Argument `covariance` must be 1D or 2D array")
 
         self.C_D = covariance
-        assert isinstance(self.C_D, np.ndarray) and self.C_D.ndim in (1, 2)
 
     def num_assimilations(self) -> int:
         return len(self.alpha)