diff --git a/FDTD/extensions/operator_ext_conductingsheet.h b/FDTD/extensions/operator_ext_conductingsheet.h
index 9a7d12d..f84dc4b 100644
--- a/FDTD/extensions/operator_ext_conductingsheet.h
+++ b/FDTD/extensions/operator_ext_conductingsheet.h
@@ -38,6 +38,7 @@ public:
 
 	virtual bool IsCylinderCoordsSave(bool closedAlpha, bool R0_included) const {UNUSED(closedAlpha); UNUSED(R0_included); return true;}
 	virtual bool IsCylindricalMultiGridSave(bool child) const {UNUSED(child); return true;}
+	virtual bool IsMPISave() const {return true;}
 
 	virtual string GetExtensionName() const {return string("Conducting Sheet Extension");}
 
diff --git a/FDTD/extensions/operator_ext_cylinder.h b/FDTD/extensions/operator_ext_cylinder.h
index 6ec07ff..c8dff2d 100644
--- a/FDTD/extensions/operator_ext_cylinder.h
+++ b/FDTD/extensions/operator_ext_cylinder.h
@@ -38,6 +38,9 @@ public:
 	virtual bool IsCylinderCoordsSave(bool closedAlpha, bool R0_included) const {UNUSED(closedAlpha); UNUSED(R0_included); return true;}
 	virtual bool IsCylindricalMultiGridSave(bool child) const {UNUSED(child); return true;}
 
+	// FIXME, this extension is not save or unknown to be save to use with MPI
+	virtual bool IsMPISave() const {return false;}
+
 	virtual std::string GetExtensionName() const {return std::string("Extension for the Cylinder-Coords Operator");}
 
 	virtual void ShowStat(ostream &ostr) const;
diff --git a/FDTD/extensions/operator_ext_excitation.h b/FDTD/extensions/operator_ext_excitation.h
index 9757c41..2abcef0 100644
--- a/FDTD/extensions/operator_ext_excitation.h
+++ b/FDTD/extensions/operator_ext_excitation.h
@@ -40,6 +40,7 @@ public:
 
 	virtual bool IsCylinderCoordsSave(bool closedAlpha, bool R0_included) const {UNUSED(closedAlpha); UNUSED(R0_included); return true;}
 	virtual bool IsCylindricalMultiGridSave(bool child) const {UNUSED(child); return true;}
+	virtual bool IsMPISave() const {return true;}
 
 	virtual string GetExtensionName() const {return string("Excitation Extension");}
 
diff --git a/FDTD/extensions/operator_ext_lorentzmaterial.h b/FDTD/extensions/operator_ext_lorentzmaterial.h
index 37d9b1a..b5e6e4c 100644
--- a/FDTD/extensions/operator_ext_lorentzmaterial.h
+++ b/FDTD/extensions/operator_ext_lorentzmaterial.h
@@ -36,6 +36,7 @@ public:
 
 	virtual bool IsCylinderCoordsSave(bool closedAlpha, bool R0_included) const {UNUSED(closedAlpha); UNUSED(R0_included); return true;}
 	virtual bool IsCylindricalMultiGridSave(bool child) const {UNUSED(child); return true;}
+	virtual bool IsMPISave() const {return true;}
 
 	virtual string GetExtensionName() const {return string("Drude/Lorentz Dispersive Material Extension");}
 
diff --git a/FDTD/extensions/operator_ext_mur_abc.h b/FDTD/extensions/operator_ext_mur_abc.h
index 8ffb444..ddc43c1 100644
--- a/FDTD/extensions/operator_ext_mur_abc.h
+++ b/FDTD/extensions/operator_ext_mur_abc.h
@@ -42,6 +42,7 @@ public:
 
 	virtual bool IsCylinderCoordsSave(bool closedAlpha, bool R0_included) const;
 	virtual bool IsCylindricalMultiGridSave(bool child) const;
+	virtual bool IsMPISave() const {return true;}
 
 	virtual string GetExtensionName() const {return string("Mur ABC Extension");}
 
diff --git a/FDTD/extensions/operator_ext_tfsf.h b/FDTD/extensions/operator_ext_tfsf.h
index 61e1f03..ff6f372 100644
--- a/FDTD/extensions/operator_ext_tfsf.h
+++ b/FDTD/extensions/operator_ext_tfsf.h
@@ -40,6 +40,9 @@ public:
 	virtual bool IsCylinderCoordsSave(bool closedAlpha, bool R0_included) const {UNUSED(closedAlpha); UNUSED(R0_included); return false;}
 	virtual bool IsCylindricalMultiGridSave(bool child) const {UNUSED(child); return false;}
 
+	// FIXME, this extension is not save to use with MPI
+	virtual bool IsMPISave() const {return false;}
+
 	virtual string GetExtensionName() const {return string("Total-Field/Scattered-Field Extension");}
 
 	virtual void ShowStat(ostream &ostr) const;
diff --git a/FDTD/extensions/operator_ext_upml.h b/FDTD/extensions/operator_ext_upml.h
index d865408..5256655 100644
--- a/FDTD/extensions/operator_ext_upml.h
+++ b/FDTD/extensions/operator_ext_upml.h
@@ -41,6 +41,8 @@ public:
 	//! Returns always true if base grid, Create_UPML will create proper child pml extensions.
 	virtual bool IsCylindricalMultiGridSave(bool child) const {if (child) return false; return true;}
 
+	virtual bool IsMPISave() const {return true;}
+
 	void SetBoundaryCondition(const int* BCs, const unsigned int size[6]);
 
 	void SetRange(const unsigned int start[3], const unsigned int stop[3]);
diff --git a/FDTD/extensions/operator_extension.h b/FDTD/extensions/operator_extension.h
index 794a15b..da20658 100644
--- a/FDTD/extensions/operator_extension.h
+++ b/FDTD/extensions/operator_extension.h
@@ -56,6 +56,9 @@ public:
 	//! The cylindrical multi grid operator will check whether the extension is save to use. Default is false. Derive this method to override.
 	virtual bool IsCylindricalMultiGridSave(bool child) const {UNUSED(child); return false;}
 
+	//! The MPI operator (if enabled) will check whether the extension is compatible with MPI. Default is false. Derive this method to override.
+	virtual bool IsMPISave() const {return false;}
+
 	virtual string GetExtensionName() const {return string("Abstract Operator Extension Base Class");}
 
 	virtual void ShowStat(ostream &ostr) const;
diff --git a/FDTD/operator_mpi.cpp b/FDTD/operator_mpi.cpp
index e79120e..12486e4 100644
--- a/FDTD/operator_mpi.cpp
+++ b/FDTD/operator_mpi.cpp
@@ -19,6 +19,7 @@
 #include "operator_sse_compressed.h"
 #include "engine_sse_compressed.h"
 #include "engine_mpi.h"
+#include "extensions/operator_extension.h"
 #include "tools/array_ops.h"
 #include "tools/useful.h"
 #include "mpi.h"
@@ -163,6 +164,21 @@ unsigned int Operator_MPI::GetNumberOfLines(int ny) const
 	return Operator_SSE_Compressed::GetNumberOfLines(ny)-1;
 }
 
+void Operator_MPI::AddExtension(Operator_Extension* op_ext)
+{
+	if (m_MPI_Enabled==false)
+		return Operator_SSE_Compressed::AddExtension(op_ext);
+
+	if (op_ext->IsMPISave())
+		Operator_SSE_Compressed::AddExtension(op_ext);
+	else
+	{
+		delete op_ext;
+		cerr << "Operator_MPI::AddExtension: Warning: Operator extension \"" << op_ext->GetExtensionName() << "\" is not compatible with MPI!! skipping...!" << endl;
+	}
+}
+
+
 string Operator_MPI::PrependRank(string name)
 {
 	stringstream out_name;
diff --git a/FDTD/operator_mpi.h b/FDTD/operator_mpi.h
index 9f2e2c3..341c6a6 100644
--- a/FDTD/operator_mpi.h
+++ b/FDTD/operator_mpi.h
@@ -52,6 +52,8 @@ public:
 
 	virtual unsigned int GetNumberOfLines(int ny) const;
 
+	virtual void AddExtension(Operator_Extension* op_ext);
+
 protected:
 	Operator_MPI();
 	bool m_MPI_Enabled;