diff --git a/skais/ais/ais_trajectory.py b/skais/ais/ais_trajectory.py
index 9d2da2ecd5c5ad8b30f94c9fd813e5d119d289a7..1f605ce0b77c60165efa7f0c11bd9d2eed0368d9 100644
--- a/skais/ais/ais_trajectory.py
+++ b/skais/ais/ais_trajectory.py
@@ -88,7 +88,7 @@ def __get_bounding_box__(bounding_box, positions, ref_index):
         upper_lon = center_lon + distance_to_center
         lower_lon = center_lon - distance_to_center
     elif type(bounding_box) is list:
-        if isinstance(bounding_box[0], numbers.Number):
+        if not isinstance(bounding_box[0], numbers.Number):
             upper_lon = bounding_box[1][0]
             lower_lon = bounding_box[0][0]
             upper_lat = bounding_box[1][1]