diff --git a/src/functionObjects/solvers/scalarTransport/scalarTransport.C b/src/functionObjects/solvers/scalarTransport/scalarTransport.C
index 954a5d6e4de2faa498665e4a56f6b193d5123fde..bcb02d7ec4b05ea4fb47016570dc61d6e6e1bcd2 100644
--- a/src/functionObjects/solvers/scalarTransport/scalarTransport.C
+++ b/src/functionObjects/solvers/scalarTransport/scalarTransport.C
@@ -89,7 +89,7 @@ Foam::tmp<Foam::volScalarField> Foam::functionObjects::scalarTransport::D
             turbulenceModel::propertiesName
         );
 
-        return model.nuEff();
+        return alphaD_*model.nu() + alphaDt_*model.nut();
     }
     else if (mesh_.foundObject<cmpModel>(turbulenceModel::propertiesName))
     {
@@ -98,7 +98,7 @@ Foam::tmp<Foam::volScalarField> Foam::functionObjects::scalarTransport::D
             turbulenceModel::propertiesName
         );
 
-        return model.muEff();
+        return alphaD_*model.mu() + alphaDt_*model.mut();
     }
     else
     {
@@ -169,11 +169,9 @@ bool Foam::functionObjects::scalarTransport::read(const dictionary& dict)
     rhoName_ = dict.lookupOrDefault<word>("rho", "rho");
     schemesField_ = dict.lookupOrDefault<word>("schemesField", fieldName_);
 
-    constantD_ = false;
-    if (dict.readIfPresent("D", D_))
-    {
-        constantD_ = true;
-    }
+    constantD_ = dict.readIfPresent("D", D_);
+    alphaD_ = dict.lookupOrDefault("alphat", 1.0);
+    alphaDt_ = dict.lookupOrDefault("alphaDt", 1.0);
 
     dict.readIfPresent("nCorr", nCorr_);
 
diff --git a/src/functionObjects/solvers/scalarTransport/scalarTransport.H b/src/functionObjects/solvers/scalarTransport/scalarTransport.H
index 86c92bdee77094265fad642b1223af2247bb4368..8d056cbe3a9a45a05cd3b6b39ca4ea5ec347f1eb 100644
--- a/src/functionObjects/solvers/scalarTransport/scalarTransport.H
+++ b/src/functionObjects/solvers/scalarTransport/scalarTransport.H
@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2012-2016 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2012-2017 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -30,11 +30,18 @@ Group
 Description
     Evolves a passive scalar transport equation.
 
-    - To specify the field name set the 'field' entry
+    - To specify the field name set the \c field entry
     - To employ the same numerical schemes as another field set
-      the 'schemesField' entry,
-    - The diffusivity can be set manually using the 'D' entry, or retrieved
-      from the turbulence model (if applicable).
+      the \c schemesField entry,
+    - A constant diffusivity may be specified with the \c D entry,
+
+    - Alternatively if a turbulence model is available a turbulent diffusivity
+      may be constructed from the laminar and turbulent viscosities using the
+      optional diffusivity coefficients \c alphaD and \c alphaDt (which default
+      to 1):
+      \verbatim
+          D = alphaD*nu + alphaDt*nut
+      \endverbatim
 
 See also
     Foam::functionObjects::fvMeshFunctionObject
@@ -83,6 +90,12 @@ class scalarTransport
         //- Flag to indicate whether a constant, uniform D_ is specified
         bool constantD_;
 
+        //- Laminar diffusion coefficient (optional)
+        scalar alphaD_;
+
+        //- Turbulent diffusion coefficient (optional)
+        scalar alphaDt_;
+
         //- Number of corrector iterations (optional)
         label nCorr_;