diff --git a/include/psa/crypto_struct.h b/include/psa/crypto_struct.h
index 3913551..dcc2a83 100644
--- a/include/psa/crypto_struct.h
+++ b/include/psa/crypto_struct.h
@@ -223,9 +223,28 @@
     return v;
 }
 
-struct psa_key_production_parameters_s {
+struct psa_custom_key_parameters_s {
     /* Future versions may add other fields in this structure. */
     uint32_t flags;
+};
+
+/** The default production parameters for key generation or key derivation.
+ *
+ * Calling psa_generate_key_custom() or psa_key_derivation_output_key_custom()
+ * with `custom=PSA_CUSTOM_KEY_PARAMETERS_INIT` and `custom_data_length=0` is
+ * equivalent to calling psa_generate_key() or psa_key_derivation_output_key()
+ * respectively.
+ */
+#define PSA_CUSTOM_KEY_PARAMETERS_INIT { 0 }
+
+/* This is a deprecated variant of `struct psa_custom_key_parameters_s`.
+ * It has exactly the same layout, plus an extra field which is a flexible
+ * array members. Thus a `const struct psa_key_production_parameters_s*`
+ * can be passed to any function that reads a
+ * `const struct psa_custom_key_parameters_s*`.
+ */
+struct psa_key_production_parameters_s {
+    uint32_t flags;
     uint8_t data[];
 };