diff --git a/include/form.cpp b/include/form.cpp
index 412fdef08..78b4e41d8 100755
--- a/include/form.cpp
+++ b/include/form.cpp
@@ -1169,7 +1169,7 @@ class TForm_string : public TForm_item
 
 protected:
   virtual const char* class_name() const { return "STRINGA"; }
-  virtual void print_body(ostream& out);
+  virtual void print_body(ostream& out) const;
 
   virtual void print_on(TMask& m);
   virtual void read_from(const TMask& m);
@@ -1244,7 +1244,7 @@ bool TForm_string::parse_item(TScanner& scanner)
   return TForm_item::parse_item(scanner);
 }
 
-void TForm_string::print_body(ostream& out)
+void TForm_string::print_body(ostream& out) const
 {
   TForm_item::print_body(out);
   if (_picture.not_empty())