diff --git a/src/cal_tools/agipdlib.py b/src/cal_tools/agipdlib.py
index 29879a1ea766184662dbb3c237a627e6496a864d..d58ac7ae630baa014160d7f026a523e34bd6ab6d 100644
--- a/src/cal_tools/agipdlib.py
+++ b/src/cal_tools/agipdlib.py
@@ -334,7 +334,9 @@ class AgipdCtrlRuns:
                     f" with values of {values}, respectively.")
 
     def sort_dark_runs(self):
-        """Order dark runs based on PatternTypeIndex."""
+        """Order dark runs based on run patterns for Adaptive mode
+        or gain modes for Fixed mode.
+        """
         assert len(self.runs) == 3, f"AGIPD dark runs are expected to be 3. {len(self.runs)} runs are given."  # noqa
         # Expected patterns:
         # XRay: 0, DarkHG: 1, DarkMG: 2, DarkLG: 3, PC: 4 and CS: 5.