diff --git a/tests/test_thinner.py b/tests/test_thinner.py
index 9945c9c..8d9c84b 100644
--- a/tests/test_thinner.py
+++ b/tests/test_thinner.py
@@ -3,7 +3,7 @@ import pprint
 
 from zfs_autobackup.Thinner import Thinner
 
-#randint is different in python 2 vs 3
+# randint is different in python 2 vs 3
 randint_compat = lambda lo, hi: lo + int(random.random() * (hi + 1 - lo))
 
 
@@ -23,6 +23,20 @@ class TestThinner(unittest2.TestCase):
 
         # return super().setUp()
 
+    def test_exceptions(self):
+        with self.assertRaisesRegexp(Exception, "^Invalid period"):
+            ThinnerRule("12X12m")
+
+        with self.assertRaisesRegexp(Exception, "^Invalid ttl"):
+            ThinnerRule("12d12X")
+
+        with self.assertRaisesRegexp(Exception, "^Period cant be"):
+            ThinnerRule("12d1d")
+
+        with self.assertRaisesRegexp(Exception, "^Invalid schedule"):
+            ThinnerRule("XXX")
+
+
     def test_incremental(self):
         ok=['2023-01-03 10:53:16',
             '2024-01-02 15:43:29',
diff --git a/zfs_autobackup/ThinnerRule.py b/zfs_autobackup/ThinnerRule.py
index ddec5f1..5351766 100644
--- a/zfs_autobackup/ThinnerRule.py
+++ b/zfs_autobackup/ThinnerRule.py
@@ -39,6 +39,10 @@ class ThinnerRule:
         rule_str = rule_str.lower()
         matches = re.findall("([0-9]*)([a-z]*)([0-9]*)([a-z]*)", rule_str)[0]
 
+        if '' in matches:
+            raise (Exception("Invalid schedule string: '{}'".format(rule_str)))
+
+        print(matches)
         period_amount = int(matches[0])
         period_unit = matches[1]
         ttl_amount = int(matches[2])