diff --git a/CHANGELOG.md b/CHANGELOG.md
index 88ce7d7..fdf4140 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -72,6 +72,7 @@
   way.
 * Correspondingly, the identifiers `inf`, `-inf`, and `nan` are now syntax
   errors.
+* `u128` and `i128` have been added as well-known number type annotations.
 
 ### KQL
 
diff --git a/SPEC.md b/SPEC.md
index 0886d9e..e09582a 100644
--- a/SPEC.md
+++ b/SPEC.md
@@ -218,6 +218,7 @@ Signed integers of various sizes (the number is the bit size):
 * `i16`
 * `i32`
 * `i64`
+* `i128`
 
 Unsigned integers of various sizes (the number is the bit size):
 
@@ -225,6 +226,7 @@ Unsigned integers of various sizes (the number is the bit size):
 * `u16`
 * `u32`
 * `u64`
+* `u128`
 
 Platform-dependent integer types, both signed and unsigned: