1 files changed, 5 insertions, 2 deletions
diff --git a/test.py b/test.py
index 0341bf3..a9bf401 100644
--- a/test.py
+++ b/test.py
@@ -22,9 +22,12 @@ def test(algorithm, input_kind=_DEFAULT_INPUT_KIND, length=_DEFAULT_LENGTH):
     print(output)
 
 def _parse_natural_number(s):
-    n = int(s)
+    try:
+        n = int(s)
+    except ValueError:
+        raise argparse.ArgumentTypeError('must be a non-negative integer: ' + str(s))
     if n < 0:
-        raise argparse.ArgumentTypeError('must not be a negative number')
+        raise argparse.ArgumentTypeError('must be a non-negative integer')
     return n
 
 def _parse_input_kind(s):