diff --git a/piccolo/columns/combination.py b/piccolo/columns/combination.py
index f98346afd..aa7ac6cef 100644
--- a/piccolo/columns/combination.py
+++ b/piccolo/columns/combination.py
@@ -12,6 +12,9 @@
 
 
 class CombinableMixin(object):
+
+    __slots__ = ()
+
     def __and__(self, value: Combinable) -> "And":
         return And(self, value)  # type: ignore
 
diff --git a/piccolo/query/methods/alter.py b/piccolo/query/methods/alter.py
index 0768c27c0..518eb3b81 100644
--- a/piccolo/query/methods/alter.py
+++ b/piccolo/query/methods/alter.py
@@ -72,7 +72,7 @@ def ddl(self) -> str:
 
 @dataclass
 class AddColumn(AlterColumnStatement):
-    __slots__ = ("column", "name")
+    __slots__ = ("name",)
 
     column: Column
     name: str
@@ -120,7 +120,7 @@ def ddl(self) -> str:
 
 @dataclass
 class SetDefault(AlterColumnStatement):
-    __slots__ = ("column", "value")
+    __slots__ = ("value",)
 
     column: Column
     value: t.Any