diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index 6356c58..e8f9a18 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -447,6 +447,10 @@
  * \param[in] attributes        The key attribute structure to query.
  * \param[out] data             On success, the key domain parameters.
  * \param data_size             Size of the \p data buffer in bytes.
+ *                              The buffer is guaranteed to be large
+ *                              enough if its size in bytes is at least
+ *                              the value given by
+ *                              PSA_KEY_DOMAIN_PARAMETERS_SIZE().
  * \param[out] data_length      On success, the number of bytes
  *                              that make up the key domain parameters data.
  *
diff --git a/include/psa/crypto_sizes.h b/include/psa/crypto_sizes.h
index 3c879e8..5f6282c 100644
--- a/include/psa/crypto_sizes.h
+++ b/include/psa/crypto_sizes.h
@@ -598,4 +598,36 @@
      PSA_KEY_TYPE_IS_ECC_PUBLIC_KEY(key_type) ? PSA_KEY_EXPORT_ECC_PUBLIC_KEY_MAX_SIZE(key_bits) : \
      0)
 
+/** Safe output buffer size for psa_get_key_domain_parameters().
+ *
+ * This macro returns a compile-time constant if its arguments are
+ * compile-time constants.
+ *
+ * \warning This function may call its arguments multiple times or
+ *          zero times, so you should not pass arguments that contain
+ *          side effects.
+ *
+ * \param key_type  A supported key type.
+ * \param key_bits  The size of the key in bits.
+ *
+ * \return If the parameters are valid and supported, return
+ *         a buffer size in bytes that guarantees that
+ *         psa_get_key_domain_parameters() will not fail with
+ *         #PSA_ERROR_BUFFER_TOO_SMALL.
+ *         If the parameters are a valid combination that is not supported
+ *         by the implementation, this macro either shall return either a
+ *         sensible size or 0.
+ *         If the parameters are not valid, the
+ *         return value is unspecified.
+ */
+#define PSA_KEY_DOMAIN_PARAMETERS_SIZE(key_type, key_bits)              \
+    (PSA_KEY_TYPE_IS_RSA(key_type) ? sizeof(int) :                      \
+     PSA_KEY_TYPE_IS_DH(key_type) ? PSA_DH_KEY_DOMAIN_PARAMETERS_SIZE(key_bits) : \
+     PSA_KEY_TYPE_IS_DSA(key_type) ? PSA_DSA_KEY_DOMAIN_PARAMETERS_SIZE(key_bits) : \
+     0)
+#define PSA_DH_KEY_DOMAIN_PARAMETERS_SIZE(key_bits)     \
+    (4 + (PSA_BITS_TO_BYTES(key_bits) + 5) * 3 /*without optional parts*/)
+#define PSA_DSA_KEY_DOMAIN_PARAMETERS_SIZE(key_bits)    \
+    (4 + (PSA_BITS_TO_BYTES(key_bits) + 5) * 2 /*p, g*/ + 34 /*q*/)
+
 #endif /* PSA_CRYPTO_SIZES_H */