diff --git a/src/dftbp/dftb/coulomb.F90 b/src/dftbp/dftb/coulomb.F90
index f29ec56d4b..aef49ba75c 100644
--- a/src/dftbp/dftb/coulomb.F90
+++ b/src/dftbp/dftb/coulomb.F90
@@ -2376,7 +2376,7 @@ end function derivRTerm
 
 
   !> Calculates the stress tensor derivatives of the Ewald electrostatics
-  !> Aguard and Madden J Chem Phys 119 7471 (2003)
+  !> Aguardo and Madden J Chem Phys 119 7471 (2003) doi: 10.1063/1.1605941
   subroutine invRStress(env, nAtom, coord, neighList, recPoint, alpha, volume, q, stress)
 
     !> Computational environment settings