diff --git a/openmc/deplete/cram.py b/openmc/deplete/cram.py
index 6b6a909ec1..f5f80dfdc4 100644
--- a/openmc/deplete/cram.py
+++ b/openmc/deplete/cram.py
@@ -76,7 +76,7 @@ class IPFCramSolver(DepSystemSolver):
 
         """
         A = sp.csr_matrix(A * dt, dtype=np.float64)
-        y = np.asarray(n0, dtype=np.float64)
+        y = n0.copy()
         ident = sp.eye(A.shape[0])
         for alpha, theta in zip(self.alpha, self.theta):
             y += 2*np.real(alpha*sla.spsolve(A - theta*ident, y))