diff --git a/sohstationviewer/model/reftek_data/reftek_helper.py b/sohstationviewer/model/reftek_data/reftek_helper.py
index fc467b112196552c3fb1e4d42091c3bf6c2a1659..ca29e9cbeda98e96564ad2a76f8d53c290725dca 100644
--- a/sohstationviewer/model/reftek_data/reftek_helper.py
+++ b/sohstationviewer/model/reftek_data/reftek_helper.py
@@ -163,7 +163,7 @@ def retrieve_gaps_from_stream_header(
         gaps_by_key_chan: Dict[Union[str, Tuple[str, str]],
                                Dict[str, List[List[int]]]],
         gaps: Dict[str, List[List[float]]],
-        gap_minimum,
+        gap_minimum: Optional[float],
         read_start: Optional[float],
         read_end: Optional[float]) -> Dict[str, List[List[float]]]:
     """
@@ -173,10 +173,15 @@ def retrieve_gaps_from_stream_header(
     :param streams: dict of stream header by sta, chan
     :param gaps_by_key_chan: gaps list by key and channel id
     :param gaps: gaps list by key
+    :param gap_minimum: minimum length of gaps to be detected
+    :param read_start: start time of data to be read
+    :param read_end: end time of data to be read
     """
     for sta_id in streams:
         sta_gaps = []
         gaps_by_key_chan[sta_id] = {}
+        if gap_minimum is None:
+            continue
         for chan_id in streams[sta_id]:
             stream = streams[sta_id][chan_id]
             gaps_in_stream = stream.get_gaps()
@@ -188,7 +193,8 @@ def retrieve_gaps_from_stream_header(
         gaps[sta_id] = squash_gaps(sta_gaps)
 
 
-def _check_gap(t1, t2, start, end, gap_minimum):
+def _check_gap(t1: float, t2: float, start: float, end: float,
+               gap_minimum: float) -> bool:
     """
     Check if a part of the given gap in the given time range and the gap is
         greater than gap_minimum
@@ -196,7 +202,7 @@ def _check_gap(t1, t2, start, end, gap_minimum):
     :param t2: end of given gap
     :param start: start of time range
     :param end: end of given time range
-    :param gap_minimum:
+    :param gap_minimum: minimum length of gaps to be detected
     :return: True if check is satisfied, False otherwise
     """
     t1 = t1.timestamp