diff --git a/include/haproxy/freq_ctr.h b/include/haproxy/freq_ctr.h
index 83fe90e09..93c3eaeba 100644
--- a/include/haproxy/freq_ctr.h
+++ b/include/haproxy/freq_ctr.h
@@ -29,7 +29,7 @@
 #include <haproxy/time.h>
 
 /* exported functions from freq_ctr.c */
-ullong freq_ctr_total(struct freq_ctr *ctr, uint period, int pend);
+ullong freq_ctr_total(const struct freq_ctr *ctr, uint period, int pend);
 
 /* Update a frequency counter by <inc> incremental units. It is automatically
  * rotated if the period is over. It is important that it correctly initializes
diff --git a/src/freq_ctr.c b/src/freq_ctr.c
index 974c12f9d..747a4cc4a 100644
--- a/src/freq_ctr.c
+++ b/src/freq_ctr.c
@@ -25,7 +25,7 @@
  * read_freq_ctr_period() to avoid reporting ups and downs on low-frequency
  * events when the past value is <= 1.
  */
-ullong freq_ctr_total(struct freq_ctr *ctr, uint period, int pend)
+ullong freq_ctr_total(const struct freq_ctr *ctr, uint period, int pend)
 {
 	ullong curr, past;
 	uint curr_tick;