diff --git a/include/psa/crypto_struct.h b/include/psa/crypto_struct.h
index 5639ad0..6efa8e7 100644
--- a/include/psa/crypto_struct.h
+++ b/include/psa/crypto_struct.h
@@ -356,10 +356,13 @@
 
 /* This function is declared in crypto_extra.h, which comes after this
  * header file, but we need the function here, so repeat the declaration. */
+#if !defined(PSA_SET_KEY_DOMAIN_PARAMETERS)
+#define PSA_SET_KEY_DOMAIN_PARAMETERS
 psa_status_t psa_set_key_domain_parameters(psa_key_attributes_t *attributes,
                                            psa_key_type_t type,
                                            const uint8_t *data,
                                            size_t data_length);
+#endif /* PSA_SET_KEY_DOMAIN_PARAMETERS */
 
 static inline void psa_set_key_type(psa_key_attributes_t *attributes,
                                     psa_key_type_t type)