diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index ba3be20..384286e 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -626,6 +626,9 @@
  * \param P         The point to export. This must be initialized.
  * \param format    The point format. This must be either
  *                  #MBEDTLS_ECP_PF_COMPRESSED or #MBEDTLS_ECP_PF_UNCOMPRESSED.
+ *                  (For groups without these formats, this parameter is
+ *                  ignored. But it still has to be either of the above
+ *                  values.)
  * \param olen      The address at which to store the length of
  *                  the output in Bytes. This must not be \c NULL.
  * \param buf       The output buffer. This must be a writable buffer
@@ -635,11 +638,14 @@
  * \return          \c 0 on success.
  * \return          #MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL if the output buffer
  *                  is too small to hold the point.
+ * \return          #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the point format
+ *                  or the export for the given group is not implemented.
  * \return          Another negative error code on other kinds of failure.
  */
-int mbedtls_ecp_point_write_binary( const mbedtls_ecp_group *grp, const mbedtls_ecp_point *P,
-                            int format, size_t *olen,
-                            unsigned char *buf, size_t buflen );
+int mbedtls_ecp_point_write_binary( const mbedtls_ecp_group *grp,
+                                    const mbedtls_ecp_point *P,
+                                    int format, size_t *olen,
+                                    unsigned char *buf, size_t buflen );
 
 /**
  * \brief           This function imports a point from unsigned binary data.
@@ -660,8 +666,8 @@
  * \return          \c 0 on success.
  * \return          #MBEDTLS_ERR_ECP_BAD_INPUT_DATA if the input is invalid.
  * \return          #MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
- * \return          #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the point format
- *                  is not implemented.
+ * \return          #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the import for the
+ *                  given group is not implemented.
  */
 int mbedtls_ecp_point_read_binary( const mbedtls_ecp_group *grp,
                                    mbedtls_ecp_point *P,
@@ -1107,6 +1113,8 @@
  * \return          #MBEDTLS_ERR_ECP_INVALID_KEY error if the key is
  *                  invalid.
  * \return          #MBEDTLS_ERR_MPI_ALLOC_FAILED if memory allocation failed.
+ * \return          #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the operation for
+ *                  the group is not implemented.
  * \return          Another negative error code on different kinds of failure.
  */
 int mbedtls_ecp_read_key( mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key,