diff --git a/format/spec.md b/format/spec.md
index 82d5ad884d..8a40cd8f65 100644
--- a/format/spec.md
+++ b/format/spec.md
@@ -870,7 +870,7 @@ Table metadata consists of the following fields:
 | _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_ | **`row-lineage`**           | A boolean, defaulting to false, setting whether or not to track the creation and updates to rows in the table. See [Row Lineage](#row-lineage).                                                                                                                                                                                                                                                  |
-|            |            | _optional_ | **`next-row-id`**           | A value higher than all assigned row IDs; the next snapshot's `first-row-id`. See [Row Lineage](#row-lineage).                                                                                                                                                                                                                                                                                   |
+|            |            | _optional_ | **`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.