diff --git a/tests/unittests/torture_crypto.c b/tests/unittests/torture_crypto.c
index 7c8cf55b..7c4e554e 100644
--- a/tests/unittests/torture_crypto.c
+++ b/tests/unittests/torture_crypto.c
@@ -84,6 +84,7 @@ static void torture_crypto_aes256_cbc(void **state)
             iv
     );
 
+    memset(output, '0', sizeof(output));
     cipher.decrypt(&cipher,
             aes256_cbc_encrypted,
             output,