diff --git a/ebml/EbmlCrc32.h b/ebml/EbmlCrc32.h
index 9e3a3dc..f34a385 100644
--- a/ebml/EbmlCrc32.h
+++ b/ebml/EbmlCrc32.h
@@ -57,7 +57,7 @@ const uint32 CRC32_NEGL = 0xffffffffL;
 DECLARE_EBML_BINARY(EbmlCrc32)
 	public:
 		EbmlCrc32(const EbmlCrc32 & ElementToClone);
-		bool ValidateSize() const {return (GetSize() == 4);}
+		virtual bool ValidateSize() const {return (GetSize() == 4);}
 		filepos_t RenderData(IOCallback & output, bool bForceRender, bool bKeepIntact = false);
 		filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA);
 //		filepos_t UpdateSize(bool bKeepIntact = false);
diff --git a/ebml/EbmlDate.h b/ebml/EbmlDate.h
index 13514e8..2360866 100644
--- a/ebml/EbmlDate.h
+++ b/ebml/EbmlDate.h
@@ -60,7 +60,7 @@ class EBML_DLL_API EbmlDate : public EbmlElement {
 		*/
 		int32 GetEpochDate() const {return int32(myDate/1000000000 + UnixEpochDelay);}
 
-		bool ValidateSize() const {return ((GetSize() == 8) || (GetSize() == 0));}
+		virtual bool ValidateSize() const {return ((GetSize() == 8) || (GetSize() == 0));}
 
 		/*!
 			\note no Default date handled
diff --git a/ebml/EbmlFloat.h b/ebml/EbmlFloat.h
index 2f990a9..e4b86e9 100644
--- a/ebml/EbmlFloat.h
+++ b/ebml/EbmlFloat.h
@@ -56,7 +56,7 @@ class EBML_DLL_API EbmlFloat : public EbmlElement {
 		EbmlFloat(const double DefaultValue, const Precision prec = FLOAT_32);
 		EbmlFloat(const EbmlFloat & ElementToClone);
 
-		bool ValidateSize() const 
+		virtual bool ValidateSize() const 
 		{
 			return (GetSize() == 4 || GetSize() == 8);
 		}
diff --git a/ebml/EbmlMaster.h b/ebml/EbmlMaster.h
index 856c1d5..bb83ccb 100644
--- a/ebml/EbmlMaster.h
+++ b/ebml/EbmlMaster.h
@@ -57,7 +57,7 @@ class EBML_DLL_API EbmlMaster : public EbmlElement {
 	public:
 		EbmlMaster(const EbmlSemanticContext & aContext, bool bSizeIsKnown = true);
 		EbmlMaster(const EbmlMaster & ElementToClone);
-		bool ValidateSize() const {return true;}
+		virtual bool ValidateSize() const {return true;}
 		/*!
 			\warning be carefull to clear the memory allocated in the ElementList elsewhere
 		*/
diff --git a/ebml/EbmlSInteger.h b/ebml/EbmlSInteger.h
index 810e2bb..f65ddc1 100644
--- a/ebml/EbmlSInteger.h
+++ b/ebml/EbmlSInteger.h
@@ -64,7 +64,7 @@ class EBML_DLL_API EbmlSInteger : public EbmlElement {
 		*/
 		virtual void SetDefaultSize(uint64 nDefaultSize = DEFAULT_INT_SIZE) {SetSize_(nDefaultSize);}
 
-		bool ValidateSize() const {return (GetSize() <= 8);}
+		virtual bool ValidateSize() const {return (GetSize() <= 8);}
 		filepos_t RenderData(IOCallback & output, bool bForceRender, bool bKeepIntact = false);
 		filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA);
 		filepos_t UpdateSize(bool bKeepIntact = false, bool bForceRender = false);
diff --git a/ebml/EbmlString.h b/ebml/EbmlString.h
index 69a2874..2b322f6 100644
--- a/ebml/EbmlString.h
+++ b/ebml/EbmlString.h
@@ -55,7 +55,7 @@ class EBML_DLL_API EbmlString : public EbmlElement {
 	
 		virtual ~EbmlString() {}
 	
-		bool ValidateSize() const {return true;} // any size is possible
+		virtual bool ValidateSize() const {return true;} // any size is possible
 		filepos_t RenderData(IOCallback & output, bool bForceRender, bool bKeepIntact = false);
 		filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA);
 		filepos_t UpdateSize(bool bKeepIntact = false, bool bForceRender = false);
diff --git a/ebml/EbmlUInteger.h b/ebml/EbmlUInteger.h
index b669405..dc6ac93 100644
--- a/ebml/EbmlUInteger.h
+++ b/ebml/EbmlUInteger.h
@@ -62,7 +62,7 @@ class EBML_DLL_API EbmlUInteger : public EbmlElement {
 		*/
 		virtual void SetDefaultSize(uint64 nDefaultSize = DEFAULT_UINT_SIZE) {SetSize_(nDefaultSize);}
 
-		bool ValidateSize() const {return (GetSize() <= 8);}
+		virtual bool ValidateSize() const {return (GetSize() <= 8);}
 		filepos_t RenderData(IOCallback & output, bool bForceRender, bool bKeepIntact = false);
 		filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA);
 		filepos_t UpdateSize(bool bKeepIntact = false, bool bForceRender = false);
diff --git a/ebml/EbmlUnicodeString.h b/ebml/EbmlUnicodeString.h
index 8fa066f..acb12d6 100644
--- a/ebml/EbmlUnicodeString.h
+++ b/ebml/EbmlUnicodeString.h
@@ -104,7 +104,7 @@ class EBML_DLL_API EbmlUnicodeString : public EbmlElement {
 	
 		virtual ~EbmlUnicodeString() {}
 	
-		bool ValidateSize() const {return true;} // any size is possible
+		virtual bool ValidateSize() const {return true;} // any size is possible
 		filepos_t RenderData(IOCallback & output, bool bForceRender, bool bKeepIntact = false);
 		filepos_t ReadData(IOCallback & input, ScopeMode ReadFully = SCOPE_ALL_DATA);
 		filepos_t UpdateSize(bool bKeepIntact = false, bool bForceRender = false);