diff --git a/src/main/thrift/parquet.thrift b/src/main/thrift/parquet.thrift
index e6b7ffeb..c928ad66 100644
--- a/src/main/thrift/parquet.thrift
+++ b/src/main/thrift/parquet.thrift
@@ -1005,6 +1005,8 @@ struct PageLocation {
  * Optional offsets for each data page in a ColumnChunk.
  *
  * Forms part of the page index, along with ColumnIndex.
+ *
+ * OffsetIndex may be present even if ColumnIndex is not.
  */
 struct OffsetIndex {
   /**
@@ -1026,6 +1028,8 @@ struct OffsetIndex {
  *
  * Forms part the page index, along with OffsetIndex.
  *
+ * If this structure is present, OffsetIndex must also be present.
+ *
  * For each field in this structure, <field>[i] refers to the page at
  * OffsetIndex.page_locations[i]
  */