diff --git a/pony/orm/sqltranslation.py b/pony/orm/sqltranslation.py
index 3e69f61e..14697cca 100644
--- a/pony/orm/sqltranslation.py
+++ b/pony/orm/sqltranslation.py
@@ -2164,6 +2164,8 @@ def negate(monad):
     def nonzero(monad):
         return CmpMonad('is not', monad, NoneMonad())
     def getattr(monad, attrname):
+        if isinstance(monad, ParamMonad):
+            throw(NotImplementedError, '{EXPR} for external expressions inside hybrid methods is not supported')
         entity = monad.type
         attr = entity._adict_.get(attrname) or entity._subclass_adict_.get(attrname)
         if attr is None:
@@ -2229,7 +2231,7 @@ def getsql(monad, sqlquery=None):
         attr = monad.attr
         entity = attr.entity
         pk_only = attr.pk_offset is not None
-        alias, parent_columns = monad.parent.tableref.make_join(pk_only)
+        alias, parent_columns = parent.tableref.make_join(pk_only)
         if pk_only:
             if entity._pk_is_composite_:
                 offset = attr.pk_columns_offset
@@ -2452,6 +2454,55 @@ class NoneMonad(ConstMonad):
     def __init__(monad, value=None):
         assert value is None
         ConstMonad.__init__(monad, value)
+    def cmp(monad, op, monad2):
+        return CmpMonad(op, monad, monad2)
+    def contains(monad, item, not_in=False):
+        return NoneMonad()
+    def nonzero(monad):
+        return NoneMonad()
+    def negate(monad):
+        return NoneMonad()
+    def getattr(monad, attrname):
+        return NoneMonad()
+    def len(monad):
+        return NoneMonad()
+    def count(monad, distinct=None):
+        return NumericExprMonad(int, [ ['VALUE', 0] ], nullable=False)
+    def aggregate(monad, func_name, distinct=None, sep=None):
+        return NoneMonad()
+    def __call__(monad, *args, **kwargs):
+        return NoneMonad()
+    def __getitem__(monad, key):
+        return NoneMonad()
+    def __add__(monad, monad2):
+        return NoneMonad()
+    def __sub__(monad, monad2):
+        return NoneMonad()
+    def __mul__(monad, monad2):
+        return NoneMonad()
+    def __truediv__(monad, monad2):
+        return NoneMonad()
+    def __floordiv__(monad, monad2):
+        return NoneMonad()
+    def __pow__(monad, monad2):
+        return NoneMonad()
+    def __neg__(monad):
+        return NoneMonad()
+    def __or__(monad, monad2):
+        return NoneMonad()
+    def __and__(monad, monad2):
+        return NoneMonad()
+    def __xor__(monad, monad2):
+        return NoneMonad()
+    def abs(monad):
+        return NoneMonad()
+    def to_int(monad):
+        return NoneMonad()
+    def to_str(monad):
+        return NoneMonad()
+    def to_real(monad):
+        return NoneMonad()
+
 
 class EllipsisMonad(ConstMonad):
     pass
@@ -2506,7 +2557,6 @@ class CmpMonad(BoolMonad):
     def __init__(monad, op, left, right):
         if op == '<>': op = '!='
         if left.type is NoneType:
-            assert right.type is not NoneType
             left, right = right, left
         if right.type is NoneType:
             if op == '==': op = 'is'
@@ -2530,6 +2580,8 @@ def negate(monad):
         return CmpMonad(cmp_negate[monad.op], monad.left, monad.right)
     def getsql(monad, sqlquery=None):
         op = monad.op
+        if monad.left.type is NoneType and monad.right.type is NoneType:  # in hybrid methods
+            return [['EQ' if op == 'is' else 'NE', ['VALUE', 1], ['VALUE', 1]]]
         left_sql = monad.left.getsql()
         if op == 'is':
             return [ sqland([ [ 'IS_NULL', item ] for item in left_sql ]) ]
diff --git a/pony/orm/tests/test_hybrid_methods_and_properties.py b/pony/orm/tests/test_hybrid_methods_and_properties.py
index 46657dac..2576a129 100644
--- a/pony/orm/tests/test_hybrid_methods_and_properties.py
+++ b/pony/orm/tests/test_hybrid_methods_and_properties.py
@@ -86,6 +86,12 @@ class Car(db.Entity):
     price = Required(int)
     color = Required(str)
 
+    def owner_likes_color(self):
+        return self.owner is not None and self.owner.favorite_color == self.color
+
+    def person_likes_color(self, user):
+        return user is not None and user.favorite_color == self.color
+
 
 def simple_func(person):
     return person.full_name
@@ -302,6 +308,24 @@ def test_32(self):
         q1 = select(p for p in Person if p.id < 4)
         q2 = select(p.id for p in q1 if p.property_with_incorrect_attr_reference)
 
+    @db_session
+    def test_33(self):
+        q1 = select(c.id for c in Car if c.owner_likes_color())
+        self.assertEqual(set(q1), {2})
+
+    @db_session
+    def test_34(self):
+        p = None
+        q1 = select(c.id for c in Car if c.person_likes_color(None))
+        self.assertEqual(set(q1), set())
+
+    @db_session
+    @raises_exception(NotImplementedError, 'user.favorite_color for external expressions inside hybrid methods '
+                                           'is not supported (inside Car.person_likes_color)')
+    def test_35(self):
+        p = Person[1]
+        q1 = select(c.id for c in Car if c.person_likes_color(p))
+        self.assertEqual(set(q1), {2, 5, 6})
 
 
 if __name__ == '__main__':