diff --git a/sys/net/application_layer/dhcpv6/client.c b/sys/net/application_layer/dhcpv6/client.c
index 27c7d06afb..8809bcab78 100644
--- a/sys/net/application_layer/dhcpv6/client.c
+++ b/sys/net/application_layer/dhcpv6/client.c
@@ -473,6 +473,8 @@ static inline uint32_t _irt_ms(uint16_t irt, bool greater_irt)
     if (greater_irt && (factor < 0)) {
         factor = -factor;
     }
+    /* random factor is also in ms, but it is supposed to be without unit,
+     * so we need to divide by ms */
     irt_ms += (factor * irt_ms) / MS_PER_SEC;
     return irt_ms;
 }
@@ -480,12 +482,18 @@ static inline uint32_t _irt_ms(uint16_t irt, bool greater_irt)
 static inline uint32_t _sub_rt_ms(uint32_t rt_prev_ms, uint16_t mrt)
 {
     uint32_t sub_rt_ms = (2 * rt_prev_ms) +
-                         ((get_rand_ms_factor() * rt_prev_ms) / MS_PER_SEC);
+                         /* random factor is also in ms, but it is supposed to
+                          * be without unit, so we need to divide by ms */
+                         ((int32_t)(get_rand_ms_factor() * rt_prev_ms) /
+                          (int32_t)MS_PER_SEC);
 
     if (sub_rt_ms > (mrt * MS_PER_SEC)) {
         uint32_t mrt_ms = mrt * MS_PER_SEC;
 
-        sub_rt_ms = mrt_ms + ((get_rand_ms_factor() * mrt_ms) / MS_PER_SEC);
+        /* random factor is also in ms, but it is supposed to be without unit,
+         * so we need to divide by ms */
+        sub_rt_ms = mrt_ms + ((int32_t)(get_rand_ms_factor() * mrt_ms) /
+                              (int32_t)MS_PER_SEC);
     }
     return sub_rt_ms;
 }