diff --git a/src/transportModels/incompressible/viscosityModels/HerschelBulkley/HerschelBulkley.C b/src/transportModels/incompressible/viscosityModels/HerschelBulkley/HerschelBulkley.C
index 00834a4f6..804af00ce 100644
--- a/src/transportModels/incompressible/viscosityModels/HerschelBulkley/HerschelBulkley.C
+++ b/src/transportModels/incompressible/viscosityModels/HerschelBulkley/HerschelBulkley.C
@@ -54,7 +54,7 @@ Foam::viscosityModels::HerschelBulkley::calcNu() const
     dimensionedScalar rtone("rtone", dimless/dimTime, 1.0);
     tmp<volScalarField> sr(strainRate());
     return (min(nu0_,(tau0_ + k_* rtone *( pow(tone * sr(), n_)
-        + pow(tone*tau0_/nu0_,n_))) / (max(sr(), dimensionedScalar
+        - pow(tone*tau0_/nu0_,n_))) / (max(sr(), dimensionedScalar
         ("VSMALL", dimless/dimTime, VSMALL)))));
 }