diff --git a/test/default/box_easy.c b/test/default/box_easy.c
index 09604925..e4ce8a67 100644
--- a/test/default/box_easy.c
+++ b/test/default/box_easy.c
@@ -42,5 +42,8 @@ int main(void)
             printf("\n");
     }
     printf("\n");
+
+    assert(crypto_box_easy(c, m, SIZE_MAX - 1U, nonce, bobpk, alicesk) == -1);
+
     return 0;
 }
diff --git a/test/default/secretbox_easy.c b/test/default/secretbox_easy.c
index c01d0179..df85070a 100644
--- a/test/default/secretbox_easy.c
+++ b/test/default/secretbox_easy.c
@@ -50,5 +50,8 @@ int main(void)
         if (i % 8 == 7)
             printf("\n");
     }
+
+    assert(crypto_secretbox_easy(c, m, SIZE_MAX - 1U, nonce, firstkey) == -1);
+
     return 0;
 }