diff --git a/tests/modules/telescope/test_basetelescope.py b/tests/modules/telescope/test_basetelescope.py
index 1638f416..0748d640 100644
--- a/tests/modules/telescope/test_basetelescope.py
+++ b/tests/modules/telescope/test_basetelescope.py
@@ -1,18 +1,18 @@
 import numpy as np
+from astroplan import Observer
+import astropy.units as u
+
 from pyobs.modules.telescope import DummyTelescope
 from pyobs.utils.time import Time
 
 
-def test_get_derotator_offset_from_header():
+def test_calculate_derotator_position():
     telescope = DummyTelescope()
+    telescope.observer = Observer(latitude=-32.375823 * u.deg, longitude=20.8108079 * u.deg, elevation=1798.0 * u.m)
     obstime = Time("2024-03-21T20:11:52.281735")
-    hdr = {
-        "LATITUDE": (-32.375823, None),
-        "LONGITUD": (20.810807999999998, None),
-        "HEIGHT": (1798.0000000004793, None),
-        "TEL-RA": (138.01290730636728, None),
-        "TEL-DEC": (-64.86351112618202, None),
-        "TEL-ROT": (-138.68173828124998, None),
-        "TEL-ALT": (57.24036032917521, None),
-    }
-    np.testing.assert_almost_equal(telescope._get_derotator_offset_from_header(hdr, obstime), 90.22, decimal=2)
+    ra = 138.01290730636728
+    dec = -64.86351112618202
+    tel_rot = -138.68173828124998
+    alt = 57.24036032917521
+    derot = telescope._calculate_derotator_position(ra, dec, alt, obstime)
+    np.testing.assert_almost_equal(derot - tel_rot, 90.22, decimal=2)