diff --git a/PROMS/VEPROMS User Interface/frmProcedureProperties.cs b/PROMS/VEPROMS User Interface/frmProcedureProperties.cs
index 4749b4ac..74aa2e80 100644
--- a/PROMS/VEPROMS User Interface/frmProcedureProperties.cs	
+++ b/PROMS/VEPROMS User Interface/frmProcedureProperties.cs	
@@ -434,7 +434,7 @@ namespace VEPROMS
 	  /// <param name="deflabel">label containing the default</param>
 	  private void ProcessCmbxSelectedValueChange(ComboBoxEx cmbx, string defstr, ButtonX button, Label deflabel)
 	  {
-		  if ((cmbx.SelectedIndex != -1) && defstr.Equals(cmbx.SelectedValue))
+		  if ((cmbx.SelectedIndex != -1) && defstr != null && defstr.Equals(cmbx.SelectedValue))
 		  {
 			  button.Focus();
 			  button.PerformClick();