diff --git a/infocalc.py b/infocalc.py
index c0668c0..4b74787 100755
--- a/infocalc.py
+++ b/infocalc.py
@@ -154,11 +154,11 @@ plt.plot(x, y, 'b-', label='T distribution')
 
 # Filter for which region to fill
 coloredregion = x#default fill all
-if args.lowerbound and args.upperbound:
+if args.lowerbound is not None and args.upperbound is not None:
     coloredregion = (x >= args.lowerbound) & ( x <= args.upperbound )
-elif args.upperbound:
+elif args.upperbound is not None:
     coloredregion =  x <= args.upperbound 
-elif args.lowerbound:
+elif args.lowerbound is not None:
     coloredregion = x >= args.lowerbound
     
 plt.fill_between(x, 0, y, where=coloredregion, color="grey", alpha=0.5, label="Design range",)