diff --git a/src/type-layout.md b/src/type-layout.md
index 5d75e1585a85d..080c3e56bce27 100644
--- a/src/type-layout.md
+++ b/src/type-layout.md
@@ -41,10 +41,12 @@ u8 | 1
 u16 | 2
 u32 | 4
 u64 | 8
+u128 | 16
 i8 | 1
 i16 | 2
 i32 | 4
 i64 | 8
+i128 | 16
 f32 | 4
 f64 | 8
 char | 4
diff --git a/src/types.md b/src/types.md
index 5d8285287991e..3a6c0a25bf9f8 100644
--- a/src/types.md
+++ b/src/types.md
@@ -48,14 +48,14 @@ language:
 
 The machine types are the following:
 
-* The unsigned word types `u8`, `u16`, `u32` and `u64`, with values drawn from
-  the integer intervals [0, 2^8 - 1], [0, 2^16 - 1], [0, 2^32 - 1] and
-  [0, 2^64 - 1] respectively.
-
-* The signed two's complement word types `i8`, `i16`, `i32` and `i64`, with
-  values drawn from the integer intervals [-(2^(7)), 2^7 - 1],
-  [-(2^(15)), 2^15 - 1], [-(2^(31)), 2^31 - 1], [-(2^(63)), 2^63 - 1]
-  respectively.
+* The unsigned word types `u8`, `u16`, `u32`, `u64`, and `u128` with values drawn from
+  the integer intervals [0, 2^8 - 1], [0, 2^16 - 1], [0, 2^32 - 1],
+  [0, 2^64 - 1], and [0, 2^128 - 1] respectively.
+
+* The signed two's complement word types `i8`, `i16`, `i32`, `i64`, and `i128`, with
+  values drawn from the integer intervals [-(2^7), 2^7 - 1],
+  [-(2^15), 2^15 - 1], [-(2^31), 2^31 - 1], [-(2^63), 2^63 - 1], and
+  [-(2^127), 2^127 - 1] respectively.
 
 * The IEEE 754-2008 `binary32` and `binary64` floating-point types: `f32` and
   `f64`, respectively.