diff --git a/test_suite/tests/test_de.rs b/test_suite/tests/test_de.rs
index a7eedba3..6c1f3d82 100644
--- a/test_suite/tests/test_de.rs
+++ b/test_suite/tests/test_de.rs
@@ -259,6 +259,27 @@ declare_tests! {
         0f32 => &[Token::F32(0.)],
         0f64 => &[Token::F64(0.)],
     }
+    test_small_int_to_128 {
+        1i128 => &[Token::I8(1)],
+        1i128 => &[Token::I16(1)],
+        1i128 => &[Token::I32(1)],
+        1i128 => &[Token::I64(1)],
+
+        1i128 => &[Token::U8(1)],
+        1i128 => &[Token::U16(1)],
+        1i128 => &[Token::U32(1)],
+        1i128 => &[Token::U64(1)],
+
+        1u128 => &[Token::I8(1)],
+        1u128 => &[Token::I16(1)],
+        1u128 => &[Token::I32(1)],
+        1u128 => &[Token::I64(1)],
+
+        1u128 => &[Token::U8(1)],
+        1u128 => &[Token::U16(1)],
+        1u128 => &[Token::U32(1)],
+        1u128 => &[Token::U64(1)],
+    }
     test_char {
         'a' => &[Token::Char('a')],
         'a' => &[Token::Str("a")],
diff --git a/test_suite/tests/test_ser.rs b/test_suite/tests/test_ser.rs
index d677fe35..795d65f6 100644
--- a/test_suite/tests/test_ser.rs
+++ b/test_suite/tests/test_ser.rs
@@ -586,3 +586,10 @@ fn test_enum_skipped() {
         "the enum variant Enum::SkippedMap cannot be serialized",
     );
 }
+
+#[test]
+fn test_integer128() {
+    assert_ser_tokens_error(&1i128, &[], "i128 is not supported");
+
+    assert_ser_tokens_error(&1u128, &[], "u128 is not supported");
+}