diff --git a/pygasflow/nozzles/rao_parabola_angles.py b/pygasflow/nozzles/rao_parabola_angles.py
index df3a299..c18a2c4 100644
--- a/pygasflow/nozzles/rao_parabola_angles.py
+++ b/pygasflow/nozzles/rao_parabola_angles.py
@@ -67,7 +67,10 @@ def __init__(self):
             if os.path.isfile(os.path.join(data_dir, f))]
 
         # substitute "," with "." for decimal separator
-        func = lambda s: float(s.replace(b",", b"."))
+        def func(s):
+            if isinstance(s, str):
+                return float(s.replace(",", "."))
+            return float(s.replace(b",", b"."))
         c = {
             0: func,
             1: func,