diff --git a/src/analysis/interpolation/qgsgridfilewriter.cpp b/src/analysis/interpolation/qgsgridfilewriter.cpp
index 92b04fd0a6a..422d1cfaf8e 100644
--- a/src/analysis/interpolation/qgsgridfilewriter.cpp
+++ b/src/analysis/interpolation/qgsgridfilewriter.cpp
@@ -100,7 +100,7 @@ int QgsGridFileWriter::writeFile( bool showProgressDialog )
 
   // create prj file
   QgsInterpolator::LayerData ld;
-  ld = mInterpolator->mLayerData.first();
+  ld = mInterpolator->layerData().first();
   QgsVectorLayer* vl = ld.vectorLayer;
   QString crs = vl->crs().toWkt();
   QFileInfo fi( mOutputFilePath );
diff --git a/src/analysis/interpolation/qgsinterpolator.h b/src/analysis/interpolation/qgsinterpolator.h
index 4f2ca2b8700..07e56b15517 100644
--- a/src/analysis/interpolation/qgsinterpolator.h
+++ b/src/analysis/interpolation/qgsinterpolator.h
@@ -64,6 +64,8 @@ class ANALYSIS_EXPORT QgsInterpolator
        @return 0 in case of success*/
     virtual int interpolatePoint( double x, double y, double& result ) = 0;
 
+    const QList<LayerData>& layerData() const { return mLayerData; }
+
   protected:
     /**Caches the vertex and value data from the provider. All the vertex data
      will be held in virtual memory
@@ -86,8 +88,6 @@ class ANALYSIS_EXPORT QgsInterpolator
        @param attributeValue the attribute value for interpolation (if not interpolated from z-coordinate)
      @return 0 in case of success*/
     int addVerticesToCache( QgsGeometry* geom, bool zCoord, double attributeValue );
-
-  friend class QgsGridFileWriter;
 };
 
 #endif