diff --git a/config/cert_exp_33.c b/config/cert_exp_33.c
index c4fe87dcaaa750ddb5fe19c8053b12b3a334c10f..0a87e075b0e1e9ebf743df38d27e609795b16f7a 100644
--- a/config/cert_exp_33.c
+++ b/config/cert_exp_33.c
@@ -1,3 +1,5 @@
+#include <stddef.h> // définit NULL
+
 void set_flag(int number, int *sign_flag) {
   if (NULL == sign_flag) {
     return;
@@ -8,10 +10,12 @@ void set_flag(int number, int *sign_flag) {
   } else if (number < 0) {
     *sign_flag = -1;
   }
+  Frama_C_show_each_set_flag(number, *sign_flag);
 }
 
 int is_negative(int number) {
   int sign;
   set_flag(number, &sign);
+  Frama_C_show_each_is_negative(number, sign);
   return sign < 0;
 }