diff --git a/pyscf/ao2mo/__init__.py b/pyscf/ao2mo/__init__.py
index 7ea93a4e6c..fbe646eb56 100644
--- a/pyscf/ao2mo/__init__.py
+++ b/pyscf/ao2mo/__init__.py
@@ -31,6 +31,7 @@
 import tempfile
 import numpy
 import h5py
+from pyscf import gto
 from pyscf.ao2mo import incore
 from pyscf.ao2mo import outcore
 from pyscf.ao2mo import r_outcore
@@ -143,7 +144,7 @@ def full(eri_or_mol, mo_coeff, erifile=None, dataname='eri_mo', intor='int2e',
     '''
     if isinstance(eri_or_mol, numpy.ndarray):
         return incore.full(eri_or_mol, mo_coeff, *args, **kwargs)
-    else:
+    elif isinstance(eri_or_mol, gto.MoleBase):
         if '_spinor' in intor:
             mod = r_outcore
         else:
@@ -157,6 +158,11 @@ def full(eri_or_mol, mo_coeff, erifile=None, dataname='eri_mo', intor='int2e',
                             *args, **kwargs)
         else:
             return mod.full_iofree(eri_or_mol, mo_coeff, intor, *args, **kwargs)
+    else:
+        raise RuntimeError('ERI is not available. If this is generated by mf._eri, '
+                           'the integral tensor is too big to store in memory. '
+                           'You should either increase mol.max_memory, or set '
+                           'mol.incore_anyway. See issue #2473.')
 
 def general(eri_or_mol, mo_coeffs, erifile=None, dataname='eri_mo', intor='int2e',
             *args, **kwargs):
@@ -293,7 +299,7 @@ def general(eri_or_mol, mo_coeffs, erifile=None, dataname='eri_mo', intor='int2e
     '''
     if isinstance(eri_or_mol, numpy.ndarray):
         return incore.general(eri_or_mol, mo_coeffs, *args, **kwargs)
-    else:
+    elif isinstance(eri_or_mol, gto.MoleBase):
         if '_spinor' in intor:
             mod = r_outcore
         else:
@@ -307,6 +313,11 @@ def general(eri_or_mol, mo_coeffs, erifile=None, dataname='eri_mo', intor='int2e
                                *args, **kwargs)
         else:
             return mod.general_iofree(eri_or_mol, mo_coeffs, intor, *args, **kwargs)
+    else:
+        raise RuntimeError('ERI is not available. If this is generated by mf._eri, '
+                           'the integral tensor is too big to store in memory. '
+                           'You should either increase mol.max_memory, or set '
+                           'mol.incore_anyway. See issue #2473.')
 
 def kernel(eri_or_mol, mo_coeffs, erifile=None, dataname='eri_mo', intor='int2e',
            *args, **kwargs):
diff --git a/pyscf/solvent/__init__.py b/pyscf/solvent/__init__.py
index eeba899549..c1976117fa 100644
--- a/pyscf/solvent/__init__.py
+++ b/pyscf/solvent/__init__.py
@@ -13,6 +13,9 @@
 # limitations under the License.
 
 from pyscf.solvent import ddcosmo
+from pyscf.solvent import ddpcm
+from pyscf.solvent import pcm
+from pyscf.solvent import smd
 
 def ddCOSMO(method_or_mol, solvent_obj=None, dm=None):
     '''Initialize ddCOSMO model.
@@ -58,7 +61,6 @@ def ddPCM(method_or_mol, solvent_obj=None, dm=None):
     from pyscf import gto
     from pyscf import scf, mcscf
     from pyscf import tdscf
-    from pyscf.solvent import ddpcm
 
     if isinstance(method_or_mol, gto.mole.Mole):
         return ddpcm.DDPCM(method_or_mol)
@@ -126,7 +128,6 @@ def PCM(method_or_mol, solvent_obj=None, dm=None):
     from pyscf import gto
     from pyscf import scf, mcscf
     from pyscf import tdscf
-    from pyscf.solvent import pcm
 
     if isinstance(method_or_mol, gto.mole.Mole):
         return pcm.PCM(method_or_mol)
@@ -157,7 +158,6 @@ def SMD(method_or_mol, solvent_obj=None, dm=None):
     '''
     from pyscf import gto
     from pyscf import scf
-    from pyscf.solvent import smd
 
     if isinstance(method_or_mol, gto.mole.Mole):
         return smd.SMD(method_or_mol)