diff --git a/libc/test/utils/CPP/CMakeLists.txt b/libc/test/utils/CPP/CMakeLists.txt
--- a/libc/test/utils/CPP/CMakeLists.txt
+++ b/libc/test/utils/CPP/CMakeLists.txt
@@ -20,6 +20,16 @@
     libc.utils.CPP.standalone_cpp
 )
 
+add_libc_unittest(
+  limits_test
+  SUITE
+    libc_cpp_utils_unittests
+  SRCS
+    limits_test.cpp
+  DEPENDS
+    libc.utils.CPP.standalone_cpp
+)
+
 add_libc_unittest(
   arrayref_test
   SUITE
diff --git a/libc/test/utils/CPP/limits_test.cpp b/libc/test/utils/CPP/limits_test.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/utils/CPP/limits_test.cpp
@@ -0,0 +1,54 @@
+//===-- Unittests for Limits ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "utils/CPP/Limits.h"
+#include "utils/UnitTest/Test.h"
+
+// This just checks against the C spec, almost all implementations will surpass
+// this.
+TEST(LlvmLibcLimitsTest, LimitsFollowSpec) {
+  ASSERT_GE(__llvm_libc::cpp::NumericLimits<int>::max(), 32767);
+  ASSERT_LE(__llvm_libc::cpp::NumericLimits<int>::min(), -32767);
+
+  ASSERT_GE(__llvm_libc::cpp::NumericLimits<unsigned int>::max(), 65535u);
+
+  ASSERT_GE(__llvm_libc::cpp::NumericLimits<long>::max(), 2147483647l);
+  ASSERT_LE(__llvm_libc::cpp::NumericLimits<long>::min(), -2147483647l);
+
+  ASSERT_GE(__llvm_libc::cpp::NumericLimits<unsigned long>::max(),
+            4294967295ul);
+
+  ASSERT_GE(__llvm_libc::cpp::NumericLimits<long long>::max(),
+            9223372036854775807ll);
+  ASSERT_LE(__llvm_libc::cpp::NumericLimits<long long>::min(),
+            -9223372036854775807ll);
+
+  ASSERT_GE(__llvm_libc::cpp::NumericLimits<unsigned long long>::max(),
+            18446744073709551615ull);
+}
+
+// This checks that the current environment supports 128 bit integers.
+TEST(LlvmLibcLimitsTest, Int128Works) {
+  // __int128_t max128 = -(~__int128_t(0) + 1);
+  // __int128_t min128 = ~__int128_t(0);
+  // EXPECT_GT(
+  //     __llvm_libc::cpp::NumericLimits<__int128_t>::max(),
+  //     __int128_t(__llvm_libc::cpp::NumericLimits<long long>::max()));
+  // ASSERT_EQ(__llvm_libc::cpp::NumericLimits<__int128_t>::max(), max128);
+
+  // EXPECT_LT(
+  //     __llvm_libc::cpp::NumericLimits<__int128_t>::min(),
+  //     __int128_t(__llvm_libc::cpp::NumericLimits<long long>::min()));
+  // ASSERT_EQ(__llvm_libc::cpp::NumericLimits<__int128_t>::min(), min128);
+
+  __uint128_t umax128 = ~__uint128_t(0);
+  EXPECT_GT(
+      __llvm_libc::cpp::NumericLimits<__uint128_t>::max(),
+      __uint128_t(__llvm_libc::cpp::NumericLimits<unsigned long long>::max()));
+  ASSERT_EQ(__llvm_libc::cpp::NumericLimits<__uint128_t>::max(), umax128);
+}
diff --git a/libc/utils/CPP/Limits.h b/libc/utils/CPP/Limits.h
--- a/libc/utils/CPP/Limits.h
+++ b/libc/utils/CPP/Limits.h
@@ -52,6 +52,18 @@
   static constexpr unsigned long long max() { return ULLONG_MAX; }
   static constexpr unsigned long long min() { return 0; }
 };
+template <> class NumericLimits<__uint128_t> {
+public:
+  static constexpr __uint128_t max() { return ~__uint128_t(0); }
+  static constexpr __uint128_t min() { return 0; }
+};
+// template <> class NumericLimits<__int128_t> {
+// public:
+//   static constexpr __int128_t max() {
+//     return -(~__int128_t(0) + 1);
+//   }
+//   static constexpr __int128_t min() { return ~__int128_t(0); }
+// };
 
 } // namespace cpp
 } // namespace __llvm_libc