diff --git a/src/de.rs b/src/de.rs
index a5d9e1d..71e0a61 100644
--- a/src/de.rs
+++ b/src/de.rs
@@ -118,10 +118,12 @@ impl<'de, 'a> de::Deserializer<'de> for &'a mut Deserializer<'de> {
             Token::I16(v) => visitor.visit_i16(v),
             Token::I32(v) => visitor.visit_i32(v),
             Token::I64(v) => visitor.visit_i64(v),
+            Token::I128(v) => visitor.visit_i128(v),
             Token::U8(v) => visitor.visit_u8(v),
             Token::U16(v) => visitor.visit_u16(v),
             Token::U32(v) => visitor.visit_u32(v),
             Token::U64(v) => visitor.visit_u64(v),
+            Token::U128(v) => visitor.visit_u128(v),
             Token::F32(v) => visitor.visit_f32(v),
             Token::F64(v) => visitor.visit_f64(v),
             Token::Char(v) => visitor.visit_char(v),
diff --git a/src/ser.rs b/src/ser.rs
index 245bbe8..7134739 100644
--- a/src/ser.rs
+++ b/src/ser.rs
@@ -109,6 +109,11 @@ impl<'s, 'a> ser::Serializer for &'s mut Serializer<'a> {
         Ok(())
     }
 
+    fn serialize_i128(self, v: i128) -> Result<(), Error> {
+        assert_next_token!(self, I128(v));
+        Ok(())
+    }
+
     fn serialize_u8(self, v: u8) -> Result<(), Error> {
         assert_next_token!(self, U8(v));
         Ok(())
@@ -129,6 +134,11 @@ impl<'s, 'a> ser::Serializer for &'s mut Serializer<'a> {
         Ok(())
     }
 
+    fn serialize_u128(self, v: u128) -> Result<(), Error> {
+        assert_next_token!(self, U128(v));
+        Ok(())
+    }
+
     fn serialize_f32(self, v: f32) -> Result<(), Error> {
         assert_next_token!(self, F32(v));
         Ok(())
diff --git a/src/token.rs b/src/token.rs
index 03b3b7b..d1ce306 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -47,6 +47,15 @@ pub enum Token {
     /// ```
     I64(i64),
 
+    /// A serialized `i128`.
+    ///
+    /// ```
+    /// # use serde_test::{assert_tokens, Token};
+    /// #
+    /// assert_tokens(&0i128, &[Token::I128(0)]);
+    /// ```
+    I128(i128),
+
     /// A serialized `u8`.
     ///
     /// ```
@@ -83,6 +92,15 @@ pub enum Token {
     /// ```
     U64(u64),
 
+    /// A serialized `u128`.
+    ///
+    /// ```
+    /// # use serde_test::{assert_tokens, Token};
+    /// #
+    /// assert_tokens(&0u128, &[Token::U128(0)]);
+    /// ```
+    U128(u128),
+
     /// A serialized `f32`.
     ///
     /// ```