diff --git a/kwant/solvers/sparse.py b/kwant/solvers/sparse.py
index fafb55b40f57c1995cec253065455f613a4b123b..68546232f5ab7bc1317f41579271dd68273a9783 100644
--- a/kwant/solvers/sparse.py
+++ b/kwant/solvers/sparse.py
@@ -43,7 +43,7 @@ def factorized(A, piv_tol=1.0, sym_piv_tol=1.0):
     """
 
     if not sp.isspmatrix_csc(A):
-        A = csc_matrix(A)
+        A = sp.csc_matrix(A)
 
     A.sort_indices()
     A = A.asfptype()  #upcast to a floating point format