diff --git a/src/BioHelpers_FABER/rmsd.py b/src/BioHelpers_FABER/rmsd.py
index 02eee6ed9411de1c4e35fc8025ae78e20fbd1ff9..258dc4f3b67e690ba3e4ada24cb5e3570b33bbdc 100644
--- a/src/BioHelpers_FABER/rmsd.py
+++ b/src/BioHelpers_FABER/rmsd.py
@@ -102,7 +102,7 @@ def rmsd_from_rot_tran(
     """Calculate an RMSD like value for a given set of vectors x and y with a given rotation matrix and translation vector
     Mathematical formula:
 
-    .. math:: \mathrm{RMSD} = \\frac{1}{M} \sum_{k=1..M} |\mathscr{U}\mathbf{x} + \mathbf{r} - \mathbf{y}|^2
+    .. math:: \mathrm{RMSD} = \\frac{1}{M} \sum_{k=1..M} |\mathscr{U}\mathbf{x}^k + \mathbf{r} - \mathbf{y}^k|^2
 
     **Important Note:** The translation vector differs from Kabsch algorithm, there you translate befor rotating. In Coutsias paper it is the otherway round.