diff --git a/include/psa/crypto_sizes.h b/include/psa/crypto_sizes.h
index d4182f5..8e7fa7a 100644
--- a/include/psa/crypto_sizes.h
+++ b/include/psa/crypto_sizes.h
@@ -286,7 +286,7 @@
  *                            correct size for an AEAD algorithm that it
  *                            recognizes, but does not support.
  */
-#define PSA_AEAD_FINISH_OUTPUT_SIZE(alg, plaintext_length)      \
+#define PSA_AEAD_FINISH_OUTPUT_SIZE(alg)      \
     ((size_t)0)
 
 /** The maximum size of the output of psa_aead_decrypt(), in bytes.