Index: src/natools-s_expressions-printers-pretty.adb
==================================================================
--- src/natools-s_expressions-printers-pretty.adb
+++ src/natools-s_expressions-printers-pretty.adb
@@ -912,10 +912,11 @@
                   Size := 2;
                   while Data'Length >= I loop
                      Size := Size + 1;
                      I := I * 10;
                   end loop;
+                  Size := Size + Data'Length;
                end;
          end case;
 
          if Output.Param.Quoted = When_Shorter
            and then Multi_Line_Quoted_Size (Output, Data) <= Size