Index: src/GenPoly/Box.cc
===================================================================
--- src/GenPoly/Box.cc	(revision f38e7d7a23b63a873ab0c895fc5b125449bfcf1e)
+++ src/GenPoly/Box.cc	(revision e16294d108932437878b5a12e8d2eae54d315031)
@@ -184,4 +184,6 @@
 			/// change the type of generic aggregate members to char[]
 			void mutateMembers( AggregateDecl * aggrDecl );
+			/// returns the calculated sizeof expression for ty, or nullptr for use C sizeof()
+			Expression* genSizeof( Type* ty );
 
 			/// Enters a new scope for type-variables, adding the type variables from ty
@@ -382,6 +384,6 @@
 		unsigned long n_members = 0;
 		bool firstMember = true;
-		for ( std::list< Declaration* >::const_iterator member = structDecl->get_members().begin(); member != structDecl->get_members().end(); ++member ) {
-			DeclarationWithType *dwt = dynamic_cast< DeclarationWithType * >( *member );
+		for ( Declaration* member : structDecl->get_members() ) {
+			DeclarationWithType *dwt = dynamic_cast< DeclarationWithType * >( member );
 			assert( dwt );
 			Type *memberType = dwt->get_type();
@@ -1747,12 +1749,27 @@
 		}
 
+		Expression * PolyGenericCalculator::genSizeof( Type* ty ) {
+			if ( ArrayType * aty = dynamic_cast<ArrayType *>(ty) ) {
+				// generate calculated size for possibly generic array
+				Expression * sizeofBase = genSizeof( aty->get_base() );
+				if ( ! sizeofBase ) return nullptr;
+				Expression * dim = aty->get_dimension();
+				aty->set_dimension( nullptr );
+				return makeOp( "?*?", sizeofBase, dim );
+			} else if ( findGeneric( ty ) ) {
+				// generate calculated size for generic type
+				return new NameExpr( sizeofName( mangleType( ty ) ) );
+			} else return nullptr;
+		}
+
 		Expression *PolyGenericCalculator::postmutate( SizeofExpr *sizeofExpr ) {
-			Type *ty = sizeofExpr->get_isType() ? sizeofExpr->get_type() : sizeofExpr->get_expr()->get_result();
-			if ( findGeneric( ty ) ) {
-				Expression *ret = new NameExpr( sizeofName( mangleType( ty ) ) );
+			Type *ty = sizeofExpr->get_isType() ? 
+				sizeofExpr->get_type() : sizeofExpr->get_expr()->get_result();
+			
+			Expression * gen = genSizeof( ty );
+			if ( gen ) {
 				delete sizeofExpr;
-				return ret;
-			}
-			return sizeofExpr;
+				return gen;
+			} else return sizeofExpr;
 		}