diff --git a/src/regionModels/surfaceFilmModels/submodels/thermo/filmViscosityModel/thixotropicViscosity/thixotropicViscosity.H b/src/regionModels/surfaceFilmModels/submodels/thermo/filmViscosityModel/thixotropicViscosity/thixotropicViscosity.H
index cac2112468..33a9ae5d9b 100644
--- a/src/regionModels/surfaceFilmModels/submodels/thermo/filmViscosityModel/thixotropicViscosity/thixotropicViscosity.H
+++ b/src/regionModels/surfaceFilmModels/submodels/thermo/filmViscosityModel/thixotropicViscosity/thixotropicViscosity.H
@@ -29,7 +29,7 @@ Description
     parameter \f$ \lambda \f$:
 
         \f[
-            \lambda = a(1 - \lambda)^b - c \lambda \dot{\gamma}^d
+            \frac{D\lambda}{Dt} = a(1 - \lambda)^b - c \lambda \dot{\gamma}^d
         \f]
 
     The viscosity is then calculated using the expression