diff --git a/test/unit/tcp/test_tcp.c b/test/unit/tcp/test_tcp.c
index 1b89f651..bfcfa1d9 100644
--- a/test/unit/tcp/test_tcp.c
+++ b/test/unit/tcp/test_tcp.c
@@ -206,7 +206,7 @@ START_TEST(test_tcp_fast_retx_recover)
   char data3[] = { 9, 10, 11, 12};
   char data4[] = {13, 14, 15, 16};
   char data5[] = {17, 18, 19, 20};
-  char data6[] = {21, 22, 23, 24};
+  char data6[TCP_MSS] = {21, 22, 23, 24};
   ip_addr_t remote_ip, local_ip, netmask;
   u16_t remote_port = 0x100, local_port = 0x101;
   err_t err;
diff --git a/test/unit/tcp/test_tcp_oos.c b/test/unit/tcp/test_tcp_oos.c
index 98f7098d..be611722 100644
--- a/test/unit/tcp/test_tcp_oos.c
+++ b/test/unit/tcp/test_tcp_oos.c
@@ -454,7 +454,7 @@ START_TEST(test_tcp_recv_ooseq_FIN_INSEQ)
 }
 END_TEST
 
-static char data_full_wnd[TCP_WND];
+static char data_full_wnd[TCP_WND + TCP_MSS];
 
 /** create multiple segments and pass them to tcp_input with the first segment missing
  * to simulate overruning the rxwin with ooseq queueing enabled */