diff --git a/util.c b/util.c
index 5e854a2..4446180 100644
--- a/util.c
+++ b/util.c
@@ -216,7 +216,7 @@ void sock_probe_mem(struct ctx *c)
  *
  * Return: difference in milliseconds
  */
-int timespec_diff_ms(const struct timespec *a, const struct timespec *b)
+long timespec_diff_ms(const struct timespec *a, const struct timespec *b)
 {
 	if (a->tv_nsec < b->tv_nsec) {
 		return (b->tv_nsec - a->tv_nsec) / 1000000 +
diff --git a/util.h b/util.h
index cf9c4b6..eebb027 100644
--- a/util.h
+++ b/util.h
@@ -147,7 +147,7 @@ int sock_l4(const struct ctx *c, sa_family_t af, uint8_t proto,
 	    const void *bind_addr, const char *ifname, uint16_t port,
 	    uint32_t data);
 void sock_probe_mem(struct ctx *c);
-int timespec_diff_ms(const struct timespec *a, const struct timespec *b);
+long timespec_diff_ms(const struct timespec *a, const struct timespec *b);
 void bitmap_set(uint8_t *map, unsigned bit);
 void bitmap_clear(uint8_t *map, unsigned bit);
 bool bitmap_isset(const uint8_t *map, unsigned bit);