diff --git a/MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4/MuonReadoutGeometryR4/MuonReadoutElement.h b/MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4/MuonReadoutGeometryR4/MuonReadoutElement.h
index b143644d97ca9146066a7a92704dd9d6c353b400..712433110208a8ba01027ee924185446ef96444c 100644
--- a/MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4/MuonReadoutGeometryR4/MuonReadoutElement.h
+++ b/MuonSpectrometer/MuonPhaseII/MuonDetDescr/MuonReadoutGeometryR4/MuonReadoutGeometryR4/MuonReadoutElement.h
@@ -165,9 +165,10 @@ class MuonReadoutElement : public GeoVDetectorElement, public AthMessaging, publ
 
     unsigned int storeAlignedTransforms(const ActsTrk::DetectorAlignStore& store) const override final;
 
+     friend class ActsTrk::TransformCacheDetEle<MuonGMR4::MuonReadoutElement>;
+   protected:
      /// Returns the transformation into the center of the readout volume
      Amg::Transform3D toStation(const ActsTrk::DetectorAlignStore* alignStore) const;
-   protected:
       
      /// Inserts a transfomration for caching
      template <class MuonDetImpl> StatusCode insertTransform(const IdentifierHash& hash);