diff --git a/include/psa/crypto_builtin_composites.h b/include/psa/crypto_builtin_composites.h
index ba3d253..2ba9133 100644
--- a/include/psa/crypto_builtin_composites.h
+++ b/include/psa/crypto_builtin_composites.h
@@ -120,7 +120,7 @@
     size_t MBEDTLS_PRIVATE(coordinate_bytes);
     psa_algorithm_t MBEDTLS_PRIVATE(alg);
     mbedtls_md_type_t MBEDTLS_PRIVATE(md_alg);
-    uint8_t *MBEDTLS_PRIVATE(hash);
+    uint8_t MBEDTLS_PRIVATE(hash)[PSA_BITS_TO_BYTES(PSA_VENDOR_ECC_MAX_CURVE_BITS)];
     size_t MBEDTLS_PRIVATE(hash_length);
 
 #else
@@ -150,7 +150,7 @@
     mbedtls_ecdsa_context *MBEDTLS_PRIVATE(ctx);
     mbedtls_ecdsa_restart_ctx MBEDTLS_PRIVATE(restart_ctx);
 
-    uint8_t *MBEDTLS_PRIVATE(hash);
+    uint8_t MBEDTLS_PRIVATE(hash)[PSA_BITS_TO_BYTES(PSA_VENDOR_ECC_MAX_CURVE_BITS)];
     size_t MBEDTLS_PRIVATE(hash_length);
 
     mbedtls_mpi MBEDTLS_PRIVATE(r);