diff --git a/include/psa/crypto_extra.h b/include/psa/crypto_extra.h
index 732149d..4ffd858 100644
--- a/include/psa/crypto_extra.h
+++ b/include/psa/crypto_extra.h
@@ -669,7 +669,7 @@
  *         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
+ *         by the implementation, this macro shall return either a
  *         sensible size or 0.
  *         If the parameters are not valid, the
  *         return value is unspecified.