diff --git a/python/swiftest/swiftest/io.py b/python/swiftest/swiftest/io.py
index 14742c8a5..0212785d3 100644
--- a/python/swiftest/swiftest/io.py
+++ b/python/swiftest/swiftest/io.py
@@ -1044,7 +1044,7 @@ def swifter2swiftest(swifter_param, plname="", tpname="", cbname="", conversion_
             cbname = "cb.swiftest.in"
     swiftest_param['CB_IN'] = cbname
    
-    unit_system = conversion_questions.get('UNITS', None)
+    unit_system = conversion_questions.get('UNITS', '')
     unit_type = 5
     if not unit_system:
         print(f"\nCentral body G*M = {GMcb}\n")
diff --git a/python/swiftest/tests/convert_code_type/swift2swifter/swift2swifter.py b/python/swiftest/tests/convert_code_type/swift2swifter/swift2swifter.py
index bd765d90f..b43dbd77b 100644
--- a/python/swiftest/tests/convert_code_type/swift2swifter/swift2swifter.py
+++ b/python/swiftest/tests/convert_code_type/swift2swifter/swift2swifter.py
@@ -10,5 +10,5 @@
 inparam = "param.swift.in"
 outparam = "param.swift2swifter.new"
 print(f"Reading Swift parameter {inparam} and saving it to {outparam}")
-sim = swiftest.Simulation(source=inparam, codename="Swift")
+sim = swiftest.Simulation(param_file=inparam, codename="Swift")
 oldparam = sim.convert(outparam, newcodename="Swifter", plname="pl.swift2swifter.in", tpname="tp.swift2swifter.in")
\ No newline at end of file
diff --git a/python/swiftest/tests/convert_code_type/swift2swiftest/swift2swiftest.py b/python/swiftest/tests/convert_code_type/swift2swiftest/swift2swiftest.py
index 6234dc61a..581f318ea 100644
--- a/python/swiftest/tests/convert_code_type/swift2swiftest/swift2swiftest.py
+++ b/python/swiftest/tests/convert_code_type/swift2swiftest/swift2swiftest.py
@@ -10,5 +10,5 @@
 inparam = "param.swift.in"
 outparam = "param.swift2swiftest.new"
 print(f"Reading Swift parameter {inparam} and saving it to {outparam}")
-sim = swiftest.Simulation(source=inparam, codename="Swift")
+sim = swiftest.Simulation(param_file=inparam, codename="Swift")
 oldparam = sim.convert(outparam, newcodename="Swiftest", plname="pl.swift2swiftest.in", tpname="tp.swift2swiftest.in", cbname="cb.swift2swiftest.in")
\ No newline at end of file
diff --git a/python/swiftest/tests/convert_code_type/swifter2swiftest/swifter2swiftest.py b/python/swiftest/tests/convert_code_type/swifter2swiftest/swifter2swiftest.py
index 4cc62bf8f..ff53b5113 100644
--- a/python/swiftest/tests/convert_code_type/swifter2swiftest/swifter2swiftest.py
+++ b/python/swiftest/tests/convert_code_type/swifter2swiftest/swifter2swiftest.py
@@ -10,5 +10,5 @@
 inparam = "param.swifter.in"
 outparam = "param.swifter2swiftest.new"
 print(f"Reading Swift parameter {inparam} and saving it to {outparam}")
-sim = swiftest.Simulation(source=inparam, codename="Swifter")
+sim = swiftest.Simulation(param_file=inparam, codename="Swifter")
 oldparam = sim.convert(outparam, newcodename="Swiftest", plname="pl.swifter2swiftest.in", tpname="tp.swifter2swiftest.in", cbname="cb.swifter2swiftest.in")
\ No newline at end of file
diff --git a/python/swiftest/tests/param_readers/param_readers.py b/python/swiftest/tests/param_readers/param_readers.py
index d940eecc3..d0e67a149 100644
--- a/python/swiftest/tests/param_readers/param_readers.py
+++ b/python/swiftest/tests/param_readers/param_readers.py
@@ -8,17 +8,17 @@
 inparam = "param.swift.in"
 outparam = "param.swift.new"
 print(f"Reading Swift parameter {inparam} and saving it to {outparam}")
-sim = swiftest.Simulation(source=inparam, codename="Swift")
+sim = swiftest.Simulation(param_file=inparam, codename="Swift")
 sim.write_param(outparam)
 
 inparam = "param.swifter.in"
 outparam = "param.swifter.new"
 print(f"Reading Swifter parameter {inparam} and saving it to {outparam}")
-sim = swiftest.Simulation(source=inparam, codename="Swifter")
+sim = swiftest.Simulation(param_file=inparam, codename="Swifter")
 sim.write_param(outparam)
 
 inparam = "param.swiftest.in"
 outparam = "param.swiftest.new"
 print(f"Reading Swifter parameter {inparam} and saving it to {outparam}")
-sim = swiftest.Simulation(source=inparam) # The default value of codename is "Swiftest"
+sim = swiftest.Simulation(param_file=inparam) # The default value of codename is "Swiftest"
 sim.write_param(outparam)
\ No newline at end of file