diff --git a/src/obidmscolumn.c b/src/obidmscolumn.c
index f347c96..a2eb8ac 100644
--- a/src/obidmscolumn.c
+++ b/src/obidmscolumn.c
@@ -1251,8 +1251,18 @@ void obi_ini_to_NA_values(OBIDMS_column_p column,
 					}
 					break;
 
-	case OBI_STR:   // fallthrough
-	case OBI_SEQ:   // fallthrough
+	case OBI_STR:   for (i=start;i<end;i++)
+					{
+						*(((index_t*) (column->data)) + i) = OBIIdx_NA;
+					}
+					break;
+
+	case OBI_SEQ:   for (i=start;i<end;i++)
+					{
+						*(((index_t*) (column->data)) + i) = OBIIdx_NA;
+					}
+					break;
+
 	case OBI_IDX:   for (i=start;i<end;i++)
 					{
 						*(((index_t*) (column->data)) + i) = OBIIdx_NA;