diff --git a/src/postProcessing/functionObjects/fvTools/calcFvcDiv/calcFvcDivTemplates.C b/src/postProcessing/functionObjects/fvTools/calcFvcDiv/calcFvcDivTemplates.C
index d756174..4bc7f69 100644
--- a/src/postProcessing/functionObjects/fvTools/calcFvcDiv/calcFvcDivTemplates.C
+++ b/src/postProcessing/functionObjects/fvTools/calcFvcDiv/calcFvcDivTemplates.C
@@ -44,7 +44,7 @@ void Foam::calcFvcDiv::calcDiv
 
         volScalarField& field = divField(resultName, vf.dimensions());
 
-        field = fvc::div(vf);
+        field == fvc::div(vf);
 
         processed = true;
     }
diff --git a/src/postProcessing/functionObjects/fvTools/calcFvcGrad/calcFvcGradTemplates.C b/src/postProcessing/functionObjects/fvTools/calcFvcGrad/calcFvcGradTemplates.C
index c028628..de62dd6 100644
--- a/src/postProcessing/functionObjects/fvTools/calcFvcGrad/calcFvcGradTemplates.C
+++ b/src/postProcessing/functionObjects/fvTools/calcFvcGrad/calcFvcGradTemplates.C
@@ -98,7 +98,7 @@ void Foam::calcFvcGrad::calcGrad
 
         vfGradType& field = gradField<Type>(resultName, vf.dimensions());
 
-        field = fvc::grad(vf);
+        field == fvc::grad(vf);
 
         processed = true;
     }
@@ -108,7 +108,7 @@ void Foam::calcFvcGrad::calcGrad
 
         vfGradType& field = gradField<Type>(resultName, sf.dimensions());
 
-        field = fvc::grad(sf);
+        field == fvc::grad(sf);
 
         processed = true;
     }
diff --git a/src/postProcessing/functionObjects/fvTools/calcMag/calcMagTemplates.C b/src/postProcessing/functionObjects/fvTools/calcMag/calcMagTemplates.C
index f9db936..d4dd4ac 100644
--- a/src/postProcessing/functionObjects/fvTools/calcMag/calcMagTemplates.C
+++ b/src/postProcessing/functionObjects/fvTools/calcMag/calcMagTemplates.C
@@ -87,7 +87,7 @@ void Foam::calcMag::calc
         volScalarField& field =
             magField<volScalarField>(resultName_, vf.dimensions());
 
-        field = mag(vf);
+        field == mag(vf);
 
         processed = true;
     }
@@ -98,7 +98,7 @@ void Foam::calcMag::calc
         surfaceScalarField& field =
             magField<surfaceScalarField>(resultName_, sf.dimensions());
 
-        field = mag(sf);
+        field == mag(sf);
 
         processed = true;
     }