diff --git a/format/spec.md b/format/spec.md
index 072baaa48e09..03f1c4873170 100644
--- a/format/spec.md
+++ b/format/spec.md
@@ -907,7 +907,7 @@ Table metadata consists of the following fields:
 |            | _optional_ | _optional_ | **`refs`**                  | A map of snapshot references. The map keys are the unique snapshot reference names in the table, and the map values are snapshot reference objects. There is always a `main` branch reference pointing to the `current-snapshot-id` even if the `refs` map is null.                                                                                                                              |
 | _optional_ | _optional_ | _optional_ | **`statistics`**            | A list (optional) of [table statistics](#table-statistics).                                                                                                                                                                                                                                                                                                                                      |
 | _optional_ | _optional_ | _optional_ | **`partition-statistics`**  | A list (optional) of [partition statistics](#partition-statistics).                                                                                                                                                                                                                                                                                                                              |
-|            |            | _optional_ | **`next-row-id`**           | A `long` higher than all assigned row IDs; the next snapshot's `first-row-id`. See [Row Lineage](#row-lineage).                                                                                                                                                                                                                                                                                  |
+|            |            | _required_ | **`next-row-id`**           | A `long` higher than all assigned row IDs; the next snapshot's `first-row-id`. See [Row Lineage](#row-lineage).                                                                                                                                                                                                                                                                                  |
 
 For serialization details, see Appendix C.