diff --git a/include/haproxy/freq_ctr-t.h b/include/haproxy/freq_ctr-t.h
index d5f1a8912..4eed37aab 100644
--- a/include/haproxy/freq_ctr-t.h
+++ b/include/haproxy/freq_ctr-t.h
@@ -28,11 +28,16 @@
  * period has to be known by the user. The period is measured in ticks and
  * must be at least 2 ticks long. This form is slightly more CPU intensive for
  * reads than the per-second form as it involves a divide.
+ *
+ * /!\ any change performed here will impact shm-stats-file mapping because the
+ * struct is embedded in shm_stats_file_object struct, so proceed with caution
+ * and change shm stats file version if needed. Also, fixed width integer types
+ * should be used (for portability)
  */
 struct freq_ctr {
-	unsigned int curr_tick; /* start date of current period (wrapping ticks) */
-	unsigned int curr_ctr; /* cumulated value for current period */
-	unsigned int prev_ctr; /* value for last period */
+	FIXED_SIZE(4, unsigned int, curr_tick); /* start date of current period (wrapping ticks) */
+	FIXED_SIZE(4, unsigned int, curr_ctr);  /* cumulated value for current period */
+	FIXED_SIZE(4, unsigned int, prev_ctr);  /* value for last period */
 };
 
 #endif /* _HAPROXY_FREQ_CTR_T_H */