diff --git a/icalendar-timeseries-server.json b/icalendar-timeseries-server.json
deleted file mode 100644
index 847ee7d..0000000
--- a/icalendar-timeseries-server.json
+++ /dev/null
@@ -1,32 +0,0 @@
-{
-    "addr": "127.0.0.1",
-    "port": 8090,
-    "start_delta": "-PT3H",
-    "end_delta": "P60D",
-    "cache": "PT3M",
-    "tz": "Europe/Zurich",
-    "calendars": {
-        "tlstest": {
-            "interval": "PT5M",
-            "url": "https://localhost/private.ics",
-            "ca": "/home/sebastian/tlstest/ca/ca/ca.crt",
-            "auth": {
-                "type": "tls",
-                "keyfile": "/home/sebastian/tlstest/client/combined.pem"
-            }
-        },
-        "filetest": {
-            "interval": "PT1M",
-            "url": "file:///srv/http/private.ics"
-        }
-    },
-    "key_replace": {
-        "summary": "a_summary",
-        "description": "b_description"
-    },
-    "value_replace": {
-        "summary": "{{ summary|truncate(100, end=' \\N{HORIZONTAL ELLIPSIS}') }}",
-        "description": "{{ description|truncate(100, end=' \\N{HORIZONTAL ELLIPSIS}') }}",
-        "useless_metric": "{{ start.timestamp() + end.timestamp() }}"
-    }
-}
diff --git a/icalendar_timeseries_server/config.py b/icalendar_timeseries_server/config.py
index 81cc795..c3d18df 100644
--- a/icalendar_timeseries_server/config.py
+++ b/icalendar_timeseries_server/config.py
@@ -28,7 +28,8 @@ class CalendarConfig:
 
     def __init__(self, config: Dict[str, Any], config_path: str) -> None:
         self._url: str = _keycheck('url', config, str, config_path)
-        self._scrape_interval: Duration = _parse_timedelta('interval', config, config_path, default_value='PT15M')
+        self._scrape_interval: Duration = _parse_timedelta('interval', config, config_path, default_value='PT15M',
+                                                           force_positive=True)
         self._ca: Optional[str] = _keycheck('ca', config, str, config_path, optional=True)
         auth: Dict[str, Any] = _keycheck('auth', config, dict, config_path, default_value={'type': 'none'})
         self._authtype: str = _keycheck('type', auth, str, f'{config_path}.auth',