diff --git a/src/include/sph_subs.h b/src/include/sph_subs.h
index dd3470da68ed49ebc8f8fe31d9a4b9ef22f05072..21eba3ecdb7ce3d0e2a87bf3c8454a378aeb8e26 100644
--- a/src/include/sph_subs.h
+++ b/src/include/sph_subs.h
@@ -511,6 +511,9 @@ void pwma(
 }
 
 /*! \brief C++ porting of RABAS
+ *
+ * This function computes radiation torque on the particle as a result
+ * of the difference between the extinction and the scattering contributions.
  *
  * \param inpol: `int`
  * \param li: `int`