diff --git a/tests/lwip_sock_ip/stack.c b/tests/lwip_sock_ip/stack.c
index e4c91671eb7bc55bed884a68b25757fba4b18f1f..ad6c8a459254b6d394541e02d894917a1d0dad6e 100644
--- a/tests/lwip_sock_ip/stack.c
+++ b/tests/lwip_sock_ip/stack.c
@@ -197,9 +197,16 @@ void _net_init(void)
     netif_add(&netif, &netdev, lwip_netdev_init, tcpip_input);
 #endif
 #if LWIP_IPV6
-    static const uint8_t local6[] = _TEST_ADDR6_LOCAL;
+    static const uint8_t local6_a[] = _TEST_ADDR6_LOCAL;
+    /* XXX need to copy into a stack variable. Otherwise, when just using
+     * `local6_a` this leads to weird alignment problems on some platforms with
+     * netif_add_ip6_address() below */
+    ip6_addr_t local6;
     s8_t idx;
-    netif_add_ip6_address(&netif, (ip6_addr_t *)&local6, &idx);
+
+    memcpy(&local6.addr, local6_a, sizeof(local6));
+    ip6_addr_clear_zone(&local6);
+    netif_add_ip6_address(&netif, &local6, &idx);
     for (int i = 0; i <= idx; i++) {
         netif.ip6_addr_state[i] |= IP6_ADDR_VALID;
     }
diff --git a/tests/lwip_sock_udp/stack.c b/tests/lwip_sock_udp/stack.c
index 4ac890b6e337575f90ceb25f4eca97a255d9e09d..16be189c030b8f2081cfaa32d129412e2033ff31 100644
--- a/tests/lwip_sock_udp/stack.c
+++ b/tests/lwip_sock_udp/stack.c
@@ -199,9 +199,16 @@ void _net_init(void)
     netif_add(&netif, &netdev, lwip_netdev_init, tcpip_input);
 #endif
 #if LWIP_IPV6
-    static const uint8_t local6[] = _TEST_ADDR6_LOCAL;
+    static const uint8_t local6_a[] = _TEST_ADDR6_LOCAL;
+    /* XXX need to copy into a stack variable. Otherwise, when just using
+     * `local6_a` this leads to weird alignment problems on some platforms with
+     * netif_add_ip6_address() below */
+    ip6_addr_t local6;
     s8_t idx;
-    netif_add_ip6_address(&netif, (ip6_addr_t *)&local6, &idx);
+
+    memcpy(&local6.addr, local6_a, sizeof(local6));
+    ip6_addr_clear_zone(&local6);
+    netif_add_ip6_address(&netif, &local6, &idx);
     for (int i = 0; i <= idx; i++) {
         netif.ip6_addr_state[i] |= IP6_ADDR_VALID;
     }