diff --git a/crypto_kem/test.c b/crypto_kem/test.c
index 9eb428a2..6c49d6f1 100644
--- a/crypto_kem/test.c
+++ b/crypto_kem/test.c
@@ -3,33 +3,66 @@
 #include <stdio.h>
 #include <string.h>
 
-#define NTESTS 100
+#define NTESTS 10
+
+/* allocate a bit more for all keys and messages and
+ * make sure it is not touched by the implementations.
+ */
+static void write_canary(unsigned char *d) {
+  *((uint64_t *)d) = 0x0123456789ABCDEF;
+}
+
+static int check_canary(unsigned char *d) {
+  if (*(uint64_t *)d != 0x0123456789ABCDEF)
+    return -1;
+  else
+    return 0;
+}
+
+static int test_keys(void) {
+  unsigned char key_a[CRYPTO_BYTES + 16], key_b[CRYPTO_BYTES + 16];
+  unsigned char pk[CRYPTO_PUBLICKEYBYTES + 16];
+  unsigned char sendb[CRYPTO_CIPHERTEXTBYTES + 16];
+  unsigned char sk_a[CRYPTO_SECRETKEYBYTES + 16];
+
+  write_canary(key_a);
+  write_canary(key_a + sizeof(key_a) - 8);
+  write_canary(key_b);
+  write_canary(key_b + sizeof(key_b) - 8);
+  write_canary(pk);
+  write_canary(pk + sizeof(pk) - 8);
+  write_canary(sendb);
+  write_canary(sendb + sizeof(sendb) - 8);
+  write_canary(sk_a);
+  write_canary(sk_a + sizeof(sk_a) - 8);
 
-int test_keys() {
-  unsigned char key_a[CRYPTO_BYTES], key_b[CRYPTO_BYTES];
-  unsigned char pk[CRYPTO_PUBLICKEYBYTES];
-  unsigned char sendb[CRYPTO_CIPHERTEXTBYTES];
-  unsigned char sk_a[CRYPTO_SECRETKEYBYTES];
   int i;
 
   for (i = 0; i < NTESTS; i++) {
     // Alice generates a public key
-    crypto_kem_keypair(pk, sk_a);
+    crypto_kem_keypair(pk + 8, sk_a + 8);
 
     // Bob derives a secret key and creates a response
-    crypto_kem_enc(sendb, key_b, pk);
+    crypto_kem_enc(sendb + 8, key_b + 8, pk + 8);
 
     // Alice uses Bobs response to get her secret key
-    crypto_kem_dec(key_a, sendb, sk_a);
+    crypto_kem_dec(key_a + 8, sendb + 8, sk_a + 8);
 
-    if (memcmp(key_a, key_b, CRYPTO_BYTES))
-      printf("ERROR keys\n");
+    if (memcmp(key_a + 8, key_b + 8, CRYPTO_BYTES)) {
+      printf("ERROR KEYS\n");
+    } else if (check_canary(key_a) || check_canary(key_a + sizeof(key_a) - 8) ||
+               check_canary(key_b) || check_canary(key_b + sizeof(key_b) - 8) ||
+               check_canary(pk) || check_canary(pk + sizeof(pk) - 8) ||
+               check_canary(sendb) || check_canary(sendb + sizeof(sendb) - 8) ||
+               check_canary(sk_a) || check_canary(sk_a + sizeof(sk_a) - 8)) {
+      printf("ERROR canary overwritten\n");
+    }
   }
 
   return 0;
 }
 
-int test_invalid_sk_a() {
+static int test_invalid_sk_a(void) {
   unsigned char sk_a[CRYPTO_SECRETKEYBYTES];
   unsigned char key_a[CRYPTO_BYTES], key_b[CRYPTO_BYTES];
   unsigned char pk[CRYPTO_PUBLICKEYBYTES];
@@ -46,17 +79,18 @@ int test_invalid_sk_a() {
     // Replace secret key with random values
     randombytes(sk_a, CRYPTO_SECRETKEYBYTES);
 
-    // Alice uses Bobs response to get her secre key
+    // Alice uses Bobs response to get her secret key
     crypto_kem_dec(key_a, sendb, sk_a);
 
-    if (!memcmp(key_a, key_b, CRYPTO_BYTES))
+    if (!memcmp(key_a, key_b, CRYPTO_BYTES)) {
       printf("ERROR invalid sk_a\n");
+    }
   }
 
   return 0;
 }
 
-int test_invalid_ciphertext() {
+static int test_invalid_ciphertext(void) {
   unsigned char sk_a[CRYPTO_SECRETKEYBYTES];
   unsigned char key_a[CRYPTO_BYTES], key_b[CRYPTO_BYTES];
   unsigned char pk[CRYPTO_PUBLICKEYBYTES];
@@ -76,11 +110,12 @@ int test_invalid_ciphertext() {
     // Change some byte in the ciphertext (i.e., encapsulated key)
     sendb[pos % CRYPTO_CIPHERTEXTBYTES] ^= 23;
 
-    // Alice uses Bobs response to get her secre key
+    // Alice uses Bobs response to get her secret key
     crypto_kem_dec(key_a, sendb, sk_a);
 
-    if (!memcmp(key_a, key_b, CRYPTO_BYTES))
+    if (!memcmp(key_a, key_b, CRYPTO_BYTES)) {
       printf("ERROR invalid ciphertext\n");
+    }
   }
 
   return 0;
@@ -91,9 +126,5 @@ int main(void) {
   test_invalid_sk_a();
   test_invalid_ciphertext();
 
-  printf("CRYPTO_SECRETKEYBYTES:  %d\n", CRYPTO_SECRETKEYBYTES);
-  printf("CRYPTO_PUBLICKEYBYTES:  %d\n", CRYPTO_PUBLICKEYBYTES);
-  printf("CRYPTO_CIPHERTEXTBYTES: %d\n", CRYPTO_CIPHERTEXTBYTES);
-
   return 0;
-}
\ No newline at end of file
+}