diff --git a/tests/src/psa_exercise_key.c b/tests/src/psa_exercise_key.c
index c594cee..618b83f 100644
--- a/tests/src/psa_exercise_key.c
+++ b/tests/src/psa_exercise_key.c
@@ -364,8 +364,10 @@
                                               psa_key_usage_t usage,
                                               psa_algorithm_t alg)
 {
-    unsigned char plaintext[256] = "Hello, world...";
-    unsigned char ciphertext[256] = "(wabblewebblewibblewobblewubble)";
+    unsigned char plaintext[PSA_ASYMMETRIC_ENCRYPT_OUTPUT_MAX_SIZE] =
+        "Hello, world...";
+    unsigned char ciphertext[PSA_ASYMMETRIC_DECRYPT_OUTPUT_MAX_SIZE] =
+        "(wabblewebblewibblewobblewubble)";
     size_t ciphertext_length = sizeof(ciphertext);
     size_t plaintext_length = 16;