diff --git a/src/py65/assembler.py b/src/py65/assembler.py
index 2398bcc..b7e2f53 100644
--- a/src/py65/assembler.py
+++ b/src/py65/assembler.py
@@ -25,16 +25,13 @@ class Assembler:
         ['imm', re.compile(r'^#\$([0-9A-F]{2})$')]                  # "#$12"
     ]
     
-    def __init__(self, mpu=None, address_parser=None):
+    def __init__(self, mpu, address_parser=None):
         """ If a configured AddressParser is passed, symbolic addresses
         may be used in the assembly statements.
         """
         if address_parser is None:
             address_parser = AddressParser()
 
-        if mpu is None:
-            mpu = MPU()
-
         self._mpu = mpu
         self._address_parser = address_parser
 
diff --git a/src/py65/disassembler.py b/src/py65/disassembler.py
index b894f07..f27ca9d 100644
--- a/src/py65/disassembler.py
+++ b/src/py65/disassembler.py
@@ -1,5 +1,10 @@
+from py65.utils.addressing import AddressParser
+
 class Disassembler:
-    def __init__(self, mpu, address_parser):
+    def __init__(self, mpu, address_parser=None):
+        if address_parser is None:
+            address_parser = AddressParser()
+
         self._mpu = mpu
         self._address_parser = address_parser