diff --git a/check_systemd_timer.py b/check_systemd_timer.py
index f01d917..63b6a80 100755
--- a/check_systemd_timer.py
+++ b/check_systemd_timer.py
@@ -40,13 +40,13 @@ def get_next_elapse(timer_name):
                     if parts.group(4):
                         time_left = parse_systemctl_time_delta(parts.group(4))
                         if isinstance(time_left, humanfriendly.InvalidTimespan):
-                            return None, humanfriendly.InvalidTimespan
+                            return None, Exception(f'Invalid Timespan: "{parts.group(4)}"')
 
                     time_passed = 'n/a'
                     if parts.group(9):
                         time_passed = parse_systemctl_time_delta(parts.group(9))
                         if isinstance(time_passed, humanfriendly.InvalidTimespan):
-                            return None, humanfriendly.InvalidTimespan
+                            return None, Exception(f'Invalid Timespan: "{parts.group(9)}"')
 
                     timer_info = {
                         'next': datetime_object,
diff --git a/checker/humanfriendly.py b/checker/humanfriendly.py
index e6a541f..bb9b578 100644
--- a/checker/humanfriendly.py
+++ b/checker/humanfriendly.py
@@ -13,7 +13,7 @@ def parse_systemctl_time_delta(time_str: str):
     spans = []
     for part in re.findall(SYSTEMCTL_TIMESPAN_RE, time_str):
         delta = part[0]
-        if 'months' in delta:
+        if 'month' in delta:
             # humanfriendly does not support "months" so we convert it to weeks
             num = int(delta.split(' ')[0])
             delta = f'{num * 4} weeks'