diff --git a/pyscf/mcscf/newton_casscf.py b/pyscf/mcscf/newton_casscf.py
index 70458d2bf..ad8a3eef7 100644
--- a/pyscf/mcscf/newton_casscf.py
+++ b/pyscf/mcscf/newton_casscf.py
@@ -442,6 +442,24 @@ def _df_jk_from_low_rank_dm(with_df, factor_pairs):
     return vj, vk
 
 
+def _materialize_eris_ppaa_papa(eris, max_memory):
+    ppaa = eris.ppaa
+    papa = eris.papa
+    if isinstance(ppaa, numpy.ndarray) and isinstance(papa, numpy.ndarray):
+        return eris
+
+    try:
+        size_mb = (ppaa.size * ppaa.dtype.itemsize +
+                   papa.size * papa.dtype.itemsize) / 1e6
+    except AttributeError:
+        return eris
+
+    if lib.current_memory()[0] + size_mb < max_memory * .9:
+        eris.ppaa = numpy.asarray(ppaa, order='C')
+        eris.papa = numpy.asarray(papa, order='C')
+    return eris
+
+
 def update_orb_ci(casscf, mo, ci0, eris, x0_guess=None,
                   conv_tol_grad=1e-4, max_stepsize=None, verbose=None):
     log = logger.new_logger(casscf, verbose)
@@ -846,6 +864,10 @@ class CASSCF(mc1step.CASSCF):
     def kernel(self, mo_coeff=None, ci0=None, callback=None):
         return mc1step.CASSCF.kernel(self, mo_coeff, ci0, callback, kernel)
 
+    def ao2mo(self, mo_coeff=None):
+        eris = mc1step.CASSCF.ao2mo(self, mo_coeff)
+        return _materialize_eris_ppaa_papa(eris, self.max_memory)
+
     def casci(self, mo_coeff, ci0=None, eris=None, verbose=None, envs=None):
         log = logger.new_logger(self, verbose)
         fcasci = mc1step._fake_h_for_fast_casci(self, mo_coeff, eris)