diff --git a/tests/lwip_sock_ip/stack.c b/tests/lwip_sock_ip/stack.c
index 7f49aecdc1ce5740e9fa6ea85eabdd339cb9b771..e4c91671eb7bc55bed884a68b25757fba4b18f1f 100644
--- a/tests/lwip_sock_ip/stack.c
+++ b/tests/lwip_sock_ip/stack.c
@@ -321,7 +321,7 @@ bool _check_4packet(uint32_t src, uint32_t dst, uint8_t proto,
                     void *data, size_t data_len, uint16_t netif)
 {
 #if LWIP_IPV4
-    msg_t msg;
+    msg_t msg = { .content = { .value = 0 } };
 
     (void)netif;
     while (data_len != (msg.content.value - sizeof(struct ip_hdr))) {
@@ -349,7 +349,7 @@ bool _check_6packet(const ipv6_addr_t *src, const ipv6_addr_t *dst,
                     uint8_t proto, void *data, size_t data_len, uint16_t netif)
 {
 #if LWIP_IPV6
-    msg_t msg;
+    msg_t msg = { .content = { .value = 0 } };
 
     (void)netif;
     while (data_len != (msg.content.value - sizeof(ipv6_hdr_t))) {
diff --git a/tests/lwip_sock_udp/stack.c b/tests/lwip_sock_udp/stack.c
index 5ee8a581df25afc185440206a41e7757a94c65c0..4ac890b6e337575f90ceb25f4eca97a255d9e09d 100644
--- a/tests/lwip_sock_udp/stack.c
+++ b/tests/lwip_sock_udp/stack.c
@@ -351,7 +351,7 @@ bool _check_4packet(uint32_t src, uint32_t dst, uint16_t src_port,
                     uint16_t netif, bool random_src_port)
 {
 #if LWIP_IPV4
-    msg_t msg;
+    msg_t msg = { .content = { .value = 0 } };
 
     (void)netif;
     while (data_len != (msg.content.value - sizeof(struct ip_hdr))) {
@@ -385,7 +385,7 @@ bool _check_6packet(const ipv6_addr_t *src, const ipv6_addr_t *dst,
                     bool random_src_port)
 {
 #if LWIP_IPV6
-    msg_t msg;
+    msg_t msg = { .content = { .value = 0 } };
 
     (void)netif;
     while (data_len != (msg.content.value - sizeof(ipv6_hdr_t))) {