diff --git a/examples/scripts/sellar_problem.py b/examples/scripts/sellar_problem.py
index ab50a30690607b87fe88d843241a80d20aff7244..21d6b052c926308fc95b55c6116d09328c6b7321 100644
--- a/examples/scripts/sellar_problem.py
+++ b/examples/scripts/sellar_problem.py
@@ -50,7 +50,7 @@ rcg.add_node('D3', category='function')
 rcg.add_node('F1', category='function', function_type='regular', sleep_time=0.)
 rcg.add_node('F2', category='function')
 rcg.add_node('G1', category='function', function_type='regular', sleep_time=0.)
-rcg.add_node('G2', category='function', function_type='regular', sleep_time=0.)
+rcg.add_node('G2', category='function', function_type='regular')
 # All variable nodes are defined
 rcg.add_node('/dataSchema/settings/a', category='variable', label='a')
 rcg.add_node('/dataSchema/settings/c', category='variable', label='c')
diff --git a/kadmos/graph/mixin_equation.py b/kadmos/graph/mixin_equation.py
index 59119fdf3c5482ab4b1147888b8404decf31d648..4a6e7a8c644612f3a4070bd7e73ad54c01abd9b4 100644
--- a/kadmos/graph/mixin_equation.py
+++ b/kadmos/graph/mixin_equation.py
@@ -3,8 +3,7 @@ import math
 import logging
 
 from ..utilities.xmls import Element
-from ..utilities.general import get_uid
-
+from ..utilities.general import get_uid, make_float_or_keep_none
 
 # Settings for the logger
 logger = logging.getLogger(__name__)
@@ -231,8 +230,8 @@ class EquationMixin(object):
             # Create mathematicalFunctions/mathematicalFunction
             cmdows_math_func = cmdows_math_funcs.add('mathematicalFunction', uID=graph_math_func)
             cmdows_math_func.add('label', self.node[graph_math_func].get('label', graph_math_func))
-            cmdows_math_func.add('functionType', self.node[graph_math_func].get('function_type', graph_math_func))
-            cmdows_math_func.add('sleepTime', self.node[graph_math_func].get('sleep_time', graph_math_func))
+            cmdows_math_func.add('functionType', self.node[graph_math_func].get('function_type'))
+            cmdows_math_func.add('sleepTime', make_float_or_keep_none(self.node[graph_math_func].get('sleep_time')))
 
             # Create mathematicalFunctions/mathematicalFunction/inputs with children
             cmdows_inputs = cmdows_math_func.add('inputs')
@@ -279,7 +278,7 @@ class EquationMixin(object):
                           shape='s',
                           label=function.findtext('label'),
                           function_type=function.findtext('functionType'),
-                          sleep_time=float(function.findtext('sleepTime')))
+                          sleep_time=make_float_or_keep_none(function.findtext('sleepTime')))
             for inp in function.findall('inputs/input'):
                 self.add_edge(inp.findtext('parameterUID').replace("'", '"'), function.get('uID'),
                               equation_label=inp.findtext('equationLabel'),
diff --git a/kadmos/utilities/general.py b/kadmos/utilities/general.py
index d8daa97e094f9cf389a7ca943673cac07a4124ff..98d1a505e749297b9ac1a51df0e00c5a76a4f15e 100644
--- a/kadmos/utilities/general.py
+++ b/kadmos/utilities/general.py
@@ -858,3 +858,12 @@ def unzip_file(file_to_unzip, destination_folder=None):
     zip_ref.extractall(destination_folder)
     zip_ref.close()
     return extracted_file
+
+
+def make_float_or_keep_none(value):
+    if isinstance(value, (float, int, str)):
+        return float(value)
+    elif value is None:
+        return None
+    else:
+        raise AssertionError('Could not process value {} which is of type {}.'.format(value, type(value)))
\ No newline at end of file