diff --git a/pyRCV2/numbers/base.py b/pyRCV2/numbers/base.py
index 9dbe759..8bdf4a3 100644
--- a/pyRCV2/numbers/base.py
+++ b/pyRCV2/numbers/base.py
@@ -168,6 +168,8 @@ class BaseNum:
 class BasePyNum(BaseNum):
 	"""Helper class for Num wrappers of Python objects that already implement overloading"""
 	
+	__slots__ = []
+	
 	_py_class = None # Subclasses must specify
 	
 	@classmethod
diff --git a/pyRCV2/numbers/fixed_py.py b/pyRCV2/numbers/fixed_py.py
index 8abde83..2e64dad 100644
--- a/pyRCV2/numbers/fixed_py.py
+++ b/pyRCV2/numbers/fixed_py.py
@@ -29,6 +29,8 @@ class Fixed(BasePyNum):
 	Wrapper for Python Decimal (for fixed-point arithmetic)
 	"""
 	
+	__slots__ = []
+	
 	_py_class = decimal.Decimal # For BasePyNum
 	
 	ROUND_DOWN = decimal.ROUND_DOWN
diff --git a/pyRCV2/numbers/gfixed_py.py b/pyRCV2/numbers/gfixed_py.py
index 49afb08..233c409 100644
--- a/pyRCV2/numbers/gfixed_py.py
+++ b/pyRCV2/numbers/gfixed_py.py
@@ -34,6 +34,8 @@ class FixedGuarded(BasePyNum):
 	Implements guarded (quasi-exact) fixed-point
 	"""
 	
+	__slots__ = []
+	
 	_py_class = decimal.Decimal # For BasePyNum
 	
 	ROUND_DOWN = decimal.ROUND_DOWN
diff --git a/pyRCV2/numbers/native_py.py b/pyRCV2/numbers/native_py.py
index c6908ee..6dfb23a 100644
--- a/pyRCV2/numbers/native_py.py
+++ b/pyRCV2/numbers/native_py.py
@@ -23,6 +23,8 @@ class Native(BasePyNum):
 	Wrapper for Python float (naive floating-point arithmetic)
 	"""
 	
+	__slots__ = []
+	
 	_py_class = float # For BasePyNum
 	
 	def round(self, dps, mode):
diff --git a/pyRCV2/numbers/rational_py.py b/pyRCV2/numbers/rational_py.py
index 9b4de4c..7b62eba 100644
--- a/pyRCV2/numbers/rational_py.py
+++ b/pyRCV2/numbers/rational_py.py
@@ -24,6 +24,8 @@ class Rational(BasePyNum):
 	Wrapper for Python Fraction (rational arithmetic)
 	"""
 	
+	__slots__ = []
+	
 	_py_class = Fraction # For BasePyNum
 	
 	def pp(self, dp):