diff --git a/GUI/panels/pdsim_panels.py b/GUI/panels/pdsim_panels.py
index 9f1d9e8..439bdf5 100644
--- a/GUI/panels/pdsim_panels.py
+++ b/GUI/panels/pdsim_panels.py
@@ -2373,7 +2373,7 @@ def OnAddFluid(self, event = None):
             # Check that you can get the molar mass of this fluid
             Fluid = dlg.GetValue().encode('ascii')
             dlg.Destroy()
-            if 'BICUBIC' in Fluid or 'TTSE' in Fluid:
+            if b'BICUBIC' in Fluid or b'TTSE' in Fluid:
                 dlg3 = wx.MessageDialog(None,"Warning: If tables have not been created already for this fluid, it will take a while to build the tables")
                 dlg3.ShowModal()
                 dlg3.Destroy()