diff --git a/meshLibrary/utilities/anisotropicMeshing/coordinateModification/boxScaling.H b/meshLibrary/utilities/anisotropicMeshing/coordinateModification/boxScaling.H
index 7c4588deb6c997560771a67704b16e303094d8b2..f741fa56c7cbf2e3fdeb8d6945b93bcdc0904848 100644
--- a/meshLibrary/utilities/anisotropicMeshing/coordinateModification/boxScaling.H
+++ b/meshLibrary/utilities/anisotropicMeshing/coordinateModification/boxScaling.H
@@ -46,6 +46,10 @@ namespace Foam
 namespace Module
 {
 
+// Forward declarations
+class boxScaling;
+Ostream& operator<<(Ostream&, const boxScaling&);
+
 /*---------------------------------------------------------------------------*\
                          Class boxScaling Declaration
 \*---------------------------------------------------------------------------*/
diff --git a/meshLibrary/utilities/containers/VRWGraph/VRWGraph.H b/meshLibrary/utilities/containers/VRWGraph/VRWGraph.H
index 2e4177644857ff667967b226d3f826aed1b3afd6..ce5cce575ff6b4a26957f3e486ab3ec84137046f 100644
--- a/meshLibrary/utilities/containers/VRWGraph/VRWGraph.H
+++ b/meshLibrary/utilities/containers/VRWGraph/VRWGraph.H
@@ -51,7 +51,9 @@ namespace Foam
 namespace Module
 {
 
+// Forward declarations
 class VRWGraph;
+Ostream& operator<<(Ostream&, const VRWGraph&);
 
 class rowElement
 {
diff --git a/meshLibrary/utilities/containers/VRWGraphList/VRWGraphList.H b/meshLibrary/utilities/containers/VRWGraphList/VRWGraphList.H
index 930c8556cd7c4de0bd756ab0720016b1a91338d9..1f20c2c68d7c7e164122e5b3ded3badb66f296d3 100644
--- a/meshLibrary/utilities/containers/VRWGraphList/VRWGraphList.H
+++ b/meshLibrary/utilities/containers/VRWGraphList/VRWGraphList.H
@@ -47,6 +47,10 @@ namespace Foam
 namespace Module
 {
 
+// Forward declarations
+class VRWGraphList;
+Ostream& operator<<(Ostream&, const VRWGraphList&);
+
 /*---------------------------------------------------------------------------*\
                         Class VRWGraphList Declaration
 \*---------------------------------------------------------------------------*/