diff --git a/src/pycalphad_xml/parser.py b/src/pycalphad_xml/parser.py
index b51f6ae..d89cee7 100644
--- a/src/pycalphad_xml/parser.py
+++ b/src/pycalphad_xml/parser.py
@@ -11,20 +11,21 @@
 from pathlib import Path
 this_dir = Path(__file__).parent
 
+def _stringify_node_text(node):
+    return ''.join(node.xpath('./text()')).replace('\n', '').replace(' ', '').strip()
 
-def convert_math_to_symbolic(math_nodes):
+
+def convert_math_to_symbolic(math_node):
     result = 0.0
-    interval_nodes = [x for x in math_nodes if (not isinstance(x, str)) and x.tag == 'Interval']
-    string_nodes = [x for x in math_nodes if isinstance(x, str)]
-    for math_node in string_nodes:
-        # +0 is a hack, for how the function works
-        result += _sympify_string(math_node+'+0')
-    result += convert_intervals_to_piecewise(interval_nodes)
+    interval_nodes = [x for x in math_node if x.tag == 'Interval']
+    # +0 is a hack, for how the function works
+    result += _sympify_string(_stringify_node_text(math_node)+'+0')
+    result += _convert_intervals_to_piecewise(interval_nodes)
     result = result.xreplace({Symbol('T'): v.T, Symbol('P'): v.P})
     return result
 
 
-def convert_intervals_to_piecewise(interval_nodes):
+def _convert_intervals_to_piecewise(interval_nodes):
     exprs = []
     conds = []
     for interval_node in interval_nodes:
@@ -33,7 +34,7 @@ def convert_intervals_to_piecewise(interval_nodes):
         variable = interval_node.attrib['in']
         lower = float(interval_node.attrib.get('lower', '-inf'))
         upper = float(interval_node.attrib.get('upper', 'inf'))
-        math_expr = convert_math_to_symbolic([''.join(interval_node.itertext()).replace('\n', '').replace(' ', '').strip()])
+        math_expr = _sympify_string(_stringify_node_text(interval_node)+'+0')
         if upper != float('inf'):
             cond = And(lower <= getattr(v, variable, Symbol(variable)), upper > getattr(v, variable))
         else:
@@ -181,9 +182,7 @@ def parse_model(dbf, phase_name, model_node, parameters):
             constituent_array = [[str(c) for c in sorted(lx)] for lx in constituent_array]
 
         # Parameter value
-        # Interval _and_ text (if any) to be able to handle intervals or scalar expressions
-        param_nodes = param_node.xpath('./Interval') + [''.join(param_node.xpath('./text()')).strip()]
-        function_obj = convert_math_to_symbolic(param_nodes)
+        function_obj = convert_math_to_symbolic(param_node)
 
         # TODO: Reference
 
@@ -254,9 +253,7 @@ def read_xml(dbf, fd):
             dbf.species.add(v.Species(species, constituent_dict, charge=species_charge))
         elif child.tag == 'Expr':
             function_name = str(child.attrib['id'])
-            # Interval _and_ text (if any) to be able to handle intervals or scalar expressions
-            expr_nodes = child.xpath('./Interval') + [''.join(child.xpath('./text()')).strip()]
-            function_obj = convert_math_to_symbolic(expr_nodes)
+            function_obj = convert_math_to_symbolic(child)
             _setitem_raise_duplicates(dbf.symbols, function_name, function_obj)
         elif child.tag == 'Phase':
             model_nodes = child.xpath('./Model')