diff --git a/python/erc20_demurrage_token/sim/sim.py b/python/erc20_demurrage_token/sim/sim.py
index 89610c7..d689e95 100644
--- a/python/erc20_demurrage_token/sim/sim.py
+++ b/python/erc20_demurrage_token/sim/sim.py
@@ -2,6 +2,7 @@
 import logging
 
 # external imports
+from chainlib.chain import ChainSpec
 from chainlib.eth.unittest.ethtester import create_tester_signer
 from chainlib.eth.unittest.base import TestRPCConnection
 from chainlib.eth.tx import (
@@ -35,8 +36,8 @@ logg = logging.getLogger(__name__)
 
 class DemurrageTokenSimulation:
 
-    def __init__(self, chain_spec, settings, redistribute=True, cap=0, actors=1):
-        self.chain_spec = chain_spec
+    def __init__(self, chain_str, settings, redistribute=True, cap=0, actors=1):
+        self.chain_spec = ChainSpec.from_chain_str(chain_str)
         self.accounts = []
         self.keystore = DictKeystore()
         self.signer = EIP155Signer(self.keystore)
@@ -76,7 +77,7 @@ class DemurrageTokenSimulation:
         self.start_timestamp = self.last_timestamp
         nonce_oracle = RPCNonceOracle(self.accounts[0], conn=self.rpc)
 
-        c = DemurrageToken(chain_spec, signer=self.signer, nonce_oracle=nonce_oracle)
+        c = DemurrageToken(self.chain_spec, signer=self.signer, nonce_oracle=nonce_oracle)
         (tx_hash, o) = c.constructor(self.accounts[0], settings, redistribute=redistribute, cap=cap)
         self.rpc.do(o)
         o = receipt(tx_hash)
diff --git a/python/tests/sim/tests_sim.py b/python/tests/sim/tests_sim.py
index 1ff19ea..1f354d2 100644
--- a/python/tests/sim/tests_sim.py
+++ b/python/tests/sim/tests_sim.py
@@ -2,9 +2,6 @@
 import unittest
 import logging
 
-# external imports
-from chainlib.chain import ChainSpec
-
 # local imports
 from erc20_demurrage_token import DemurrageTokenSettings
 from erc20_demurrage_token.sim import DemurrageTokenSimulation
@@ -16,7 +13,6 @@ logg = logging.getLogger()
 class TestSim(unittest.TestCase):
 
     def setUp(self):
-        self.chain_spec = ChainSpec('evm', 'foochain', 42)
         self.cap = 0
         settings = DemurrageTokenSettings()
         settings.name = 'Simulated Demurrage Token'
@@ -24,7 +20,7 @@ class TestSim(unittest.TestCase):
         settings.decimals = 6
         settings.demurrage_level = 5010590837337300000000000000000000 # equals approx 2% per month
         settings.period_minutes = 10800 # 1 week in minutes
-        self.sim = DemurrageTokenSimulation(self.chain_spec, settings, redistribute=True, cap=self.cap, actors=10)
+        self.sim = DemurrageTokenSimulation('evm:foochain:42', settings, redistribute=True, cap=self.cap, actors=10)
 
 
     def test_mint(self):
diff --git a/python/tests/sim/tests_sim_limit.py b/python/tests/sim/tests_sim_limit.py
index bb53b30..ea3bfae 100644
--- a/python/tests/sim/tests_sim_limit.py
+++ b/python/tests/sim/tests_sim_limit.py
@@ -2,9 +2,6 @@
 import unittest
 import logging
 
-# external imports
-from chainlib.chain import ChainSpec
-
 # local imports
 from erc20_demurrage_token import DemurrageTokenSettings
 from erc20_demurrage_token.sim import (
@@ -18,7 +15,6 @@ logg = logging.getLogger()
 class TestLimit(unittest.TestCase):
 
     def setUp(self):
-        self.chain_spec = ChainSpec('evm', 'foochain', 42)
         self.cap = 0
         settings = DemurrageTokenSettings()
         settings.name = 'Simulated Demurrage Token'
@@ -26,7 +22,7 @@ class TestLimit(unittest.TestCase):
         settings.decimals = 6
         settings.demurrage_level = 1
         settings.period_minutes = 1
-        self.sim = DemurrageTokenSimulation(self.chain_spec, settings, redistribute=True, cap=self.cap, actors=1)
+        self.sim = DemurrageTokenSimulation('evm:foochain:42', settings, redistribute=True, cap=self.cap, actors=1)
 
 
     def test_limit(self):