diff --git a/tests/src/psa_exercise_key.c b/tests/src/psa_exercise_key.c
index b7b507465..1b30c44c5 100644
--- a/tests/src/psa_exercise_key.c
+++ b/tests/src/psa_exercise_key.c
@@ -185,7 +185,8 @@ static int exercise_cipher_key(mbedtls_svc_key_id_t key,
     psa_key_type_t key_type;
     const unsigned char plaintext[16] = "Hello, world...";
     /* We need to tell the compiler that we meant to leave out the null character. */
-    unsigned char ciphertext[32] __attribute__ ((nonstring)) = "(wabblewebblewibblewobblewubble)";
+    unsigned char ciphertext[32] MBEDTLS_ATTRIBUTE_UNTERMINATED_STRING =
+        "(wabblewebblewibblewobblewubble)";
     size_t ciphertext_length = sizeof(ciphertext);
     unsigned char decrypted[sizeof(ciphertext)];
     size_t part_length;