diff --git a/pyscf/gto/mole.py b/pyscf/gto/mole.py
index 3d8a476c45..76f5e8b95b 100644
--- a/pyscf/gto/mole.py
+++ b/pyscf/gto/mole.py
@@ -2577,11 +2577,16 @@ def build(self, dump_input=True, parse_arg=ARGPARSE,
             # number of electrons are consistent.
             self.nelec
 
-        if self.magmom is None or len(self.magmom) != self.natm:
+        if self.magmom is None:
+            self.magmom = [0,] * self.natm
+        elif len(self.magmom) != self.natm:
+            logger.warn(self, 'len(magmom) != natm. Set magmom to zero')
             self.magmom = [0,] * self.natm
         if self.spin == 0 and abs(numpy.sum(self.magmom) - self.spin) > 1e-6:
             #don't check for unrestricted calcs.
             raise ValueError("mol.magmom is set incorrectly.")
+        if isinstance(self.magmom, np.ndarray):
+            self.magmom = self.magmom.tolist()
 
         if self.symmetry:
             self._build_symmetry()
diff --git a/pyscf/pbc/gto/cell.py b/pyscf/pbc/gto/cell.py
index 49bc31f257..87282fbfd4 100644
--- a/pyscf/pbc/gto/cell.py
+++ b/pyscf/pbc/gto/cell.py
@@ -99,7 +99,8 @@ def dumps(cell):
     celldic['pseudo'] = repr(cell.pseudo)
     celldic['ecp'] = repr(cell.ecp)
     # Explicitly convert mesh because it is often created as numpy array
-    celldic['mesh'] = list(cell.mesh)
+    if isinstance(cell.mesh, np.ndarray):
+        celldic['mesh'] = cell.mesh.tolist()
 
     try:
         return json.dumps(celldic)
diff --git a/pyscf/pbc/gto/test/test_cell.py b/pyscf/pbc/gto/test/test_cell.py
index c035d271dc..5dee058140 100644
--- a/pyscf/pbc/gto/test/test_cell.py
+++ b/pyscf/pbc/gto/test/test_cell.py
@@ -84,6 +84,10 @@ def test_mixed_basis(self):
 
     def test_dumps_loads(self):
         cl1.loads(cl1.dumps())
+        # see issue 2026
+        from pyscf.pbc.tools.pbc import super_cell
+        sc = super_cell(cl1, [1,1,1])
+        sc.dumps()
 
     def test_get_lattice_Ls(self):
         #self.assertEqual(cl1.get_lattice_Ls([0,0,0]).shape, (1  , 3))
diff --git a/pyscf/pbc/tools/pbc.py b/pyscf/pbc/tools/pbc.py
index 77042a5e3a..7ca867fd21 100644
--- a/pyscf/pbc/tools/pbc.py
+++ b/pyscf/pbc/tools/pbc.py
@@ -590,7 +590,10 @@ def super_cell(cell, ncopy, wrap_around=False):
     supcell.a = np.einsum('i,ij->ij', ncopy, a)
     mesh = np.asarray(ncopy) * np.asarray(cell.mesh)
     supcell.mesh = (mesh // 2) * 2 + 1
-    supcell.magmom = list(cell.magmom) * np.prod(ncopy)
+    if isinstance(cell.magmom, np.ndarray):
+        supcell.magmom = cell.magmom.tolist() * np.prod(ncopy)
+    else:
+        supcell.magmom = cell.magmom * np.prod(ncopy)
     return _build_supcell_(supcell, cell, Ls)