diff --git a/specimen-igcse-prerelease.py b/specimen-igcse-prerelease.py
index f9e697b..1eff1cd 100644
--- a/specimen-igcse-prerelease.py
+++ b/specimen-igcse-prerelease.py
@@ -23,6 +23,9 @@ def getMark(test_number, student_index, max_mark):
                 mark = None
         else:
             mark = None
+        # if input is invalid, print error message
+        if not mark:
+            print("Invalid input. Please enter a number between 0 and %d." % max_mark)
     # return mark
     return int(mark)