diff --git a/ExprNode.hh b/ExprNode.hh
index bef4a415785c248d03c4c9b881db5da884b6b7a5..048196cae967d18e105ee443c812d06210b0b886 100644
--- a/ExprNode.hh
+++ b/ExprNode.hh
@@ -34,6 +34,7 @@ using namespace std;
 class DataTree;
 class VariableNode;
 class BinaryOpNode;
+class SymbolTable;
 
 typedef class ExprNode *expr_t;
 
diff --git a/ExternalFunctionsTable.hh b/ExternalFunctionsTable.hh
index b5218bea543ab216975c05e17a22c341a7241718..0dfe698acde7860b47884946f71f714b79473927 100644
--- a/ExternalFunctionsTable.hh
+++ b/ExternalFunctionsTable.hh
@@ -28,6 +28,7 @@ using namespace std;
 #include <map>
 
 #include "SymbolTable.hh"
+class SymbolTable;
 
 enum ExternalFunctionSetOrNot
   {