diff --git a/src/finiteVolume/cfdTools/general/MRF/MRFZone.C b/src/finiteVolume/cfdTools/general/MRF/MRFZone.C
index 8bc4d3b938..42cd06c6d5 100644
--- a/src/finiteVolume/cfdTools/general/MRF/MRFZone.C
+++ b/src/finiteVolume/cfdTools/general/MRF/MRFZone.C
@@ -29,6 +29,10 @@ License
 #include "volFields.H"
 #include "surfaceFields.H"
 #include "fvMatrices.H"
+#include "PackedList.H"
+#include "syncTools.H"
+
+#include "faceSet.H"
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
@@ -39,12 +43,15 @@ Foam::MRFZone::MRFZone(const fvMesh& mesh, Istream& is)
     dict_(is),
     cellZoneID_(mesh_.cellZones().findZoneID(name_)),
     faceZoneID_(mesh_.faceZones().findZoneID(name_)),
+    outsideFaces_(0),
     patchNames_(dict_.lookup("patches")),
     origin_(dict_.lookup("origin")),
     axis_(dict_.lookup("axis")),
     omega_(dict_.lookup("omega")),
     Omega_("Omega", omega_*axis_)
 {
+    const polyBoundaryMesh& patches = mesh_.boundaryMesh();
+
     axis_ = axis_/mag(axis_);
     Omega_ = omega_*axis_;
 
@@ -65,18 +72,78 @@ Foam::MRFZone::MRFZone(const fvMesh& mesh, Istream& is)
 
     if (!faceZoneFound)
     {
-        FatalErrorIn
+        WarningIn
         (
             "Foam::MRFZone::MRFZone(const fvMesh& , const dictionary&)"
         )   << "cannot find MRF faceZone " << name_
-            << exit(FatalError);
+            << " ; taking faces on outside of cellZone."
+            << endl;
+
+        // Determine faces in cell zone
+        // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+        // (does not construct cells)
+
+        const labelList& own = mesh_.faceOwner();
+        const labelList& nei = mesh_.faceNeighbour();
+
+        // Cells in zone
+        PackedBoolList zoneCell(mesh_.nCells());
+
+        if (cellZoneID_ != -1)
+        {
+            const labelList& cellLabels = mesh_.cellZones()[cellZoneID_];
+            forAll(cellLabels, i)
+            {
+                zoneCell[cellLabels[i]] = 1u;
+            }
+        }
+
+
+        // Faces in zone
+        PackedBoolList zoneFacesSet(mesh_.nFaces());
+
+        for (label faceI = 0; faceI < mesh_.nInternalFaces(); faceI++)
+        {
+            if
+            (
+                zoneCell.get(own[faceI]) == 1u
+             || zoneCell.get(nei[faceI]) == 1u
+            )
+            {
+                zoneFacesSet[faceI] = 1u;
+            }
+        }
+        syncTools::syncFaceList(mesh_, zoneFacesSet, orEqOp<unsigned int>());
+
+
+        // Transfer to labelList
+        label n = zoneFacesSet.count();
+        outsideFaces_.setSize(n);
+        n = 0;
+        forAll(zoneFacesSet, faceI)
+        {
+            if (zoneFacesSet.get(faceI) == 1u)
+            {
+                outsideFaces_[n++] = faceI;
+            }
+        }
+
+        Info<< nl
+            << "MRFZone " << name_ << " : found "
+            << returnReduce(outsideFaces_.size(), sumOp<label>())
+            << " faces inside cellZone." << endl;
+
+
+        // Flag use of outsideFaces
+        faceZoneID_ = -2;
     }
 
+
     patchLabels_.setSize(patchNames_.size());
 
     forAll(patchNames_, i)
     {
-        patchLabels_[i] = mesh_.boundaryMesh().findPatchID(patchNames_[i]);
+        patchLabels_[i] = patches.findPatchID(patchNames_[i]);
 
         if (patchLabels_[i] == -1)
         {
@@ -125,7 +192,13 @@ void Foam::MRFZone::relativeFlux(surfaceScalarField& phi) const
     const vector& origin = origin_.value();
     const vector& Omega = Omega_.value();
 
-    const labelList& faces = mesh_.faceZones()[faceZoneID_];
+    // Use either zone faces or outsideFaces_
+    const labelList& faces =
+    (
+        faceZoneID_ == -2
+      ? outsideFaces_
+      : mesh_.faceZones()[faceZoneID_]
+    );
 
     forAll(faces, i)
     {
diff --git a/src/finiteVolume/cfdTools/general/MRF/MRFZone.H b/src/finiteVolume/cfdTools/general/MRF/MRFZone.H
index 3ffb4e461a..7c489ed25b 100644
--- a/src/finiteVolume/cfdTools/general/MRF/MRFZone.H
+++ b/src/finiteVolume/cfdTools/general/MRF/MRFZone.H
@@ -26,7 +26,7 @@ Class
     Foam::MRFZone
 
 Description
-    MRF zone definition based on both cell and face zones and parameters
+    MRF zone definition based on cell zone and optional face zone and parameters
     obtained from a control dictionary constructed from the given stream.
 
     The rotation of the MRF region is defined by an origin and axis of
@@ -68,18 +68,26 @@ class MRFZone
 
         const fvMesh& mesh_;
 
-        word name_;
+        const word name_;
 
-        dictionary dict_;
+        const dictionary dict_;
 
         label cellZoneID_;
+
+        //- label of face zone with faces on outside of cell zone.
+        //  If -2 determines outside faces itself
         label faceZoneID_;
-        wordList patchNames_;
+
+        //- outside faces (only if faceZoneID = -2)
+        labelList outsideFaces_;
+
+
+        const wordList patchNames_;
         labelList patchLabels_;
 
-        dimensionedVector origin_;
+        const dimensionedVector origin_;
         dimensionedVector axis_;
-        dimensionedScalar omega_;
+        const dimensionedScalar omega_;
         dimensionedVector Omega_;