diff --git a/src/obidmscolumn_str.h b/src/obidmscolumn_str.h
index 4bc1d2e..06094d1 100644
--- a/src/obidmscolumn_str.h
+++ b/src/obidmscolumn_str.h
@@ -51,7 +51,7 @@ int obi_column_set_obistr_with_elt_idx(OBIDMS_column_p column, index_t line_nb,
  * @param element_idx The index of the element that should be recovered in the line.
  *
  * @returns The recovered value.
- * @retval '\0' the NA value of the type if an error occurred and obi_errno is set.
+ * @retval OBIStr_NA the NA value of the type if an error occurred and obi_errno is set.
  *
  * @since October 2015
  * @author Celine Mercier (celine.mercier@metabarcoding.org)
@@ -89,7 +89,7 @@ int obi_column_set_obistr_with_elt_name(OBIDMS_column_p column, index_t line_nb,
  * @param element_name The name of the element that should be recovered in the line.
  *
  * @returns The recovered value.
- * @retval '\0' the NA value of the type if an error occurred and obi_errno is set.
+ * @retval OBIStr_NA the NA value of the type if an error occurred and obi_errno is set.
  *
  * @since October 2015
  * @author Celine Mercier (celine.mercier@metabarcoding.org)