diff --git a/libc/test/src/math/fmaxl_test.cpp b/libc/test/src/math/fmaxl_test.cpp
@@ -0,0 +1,73 @@
+//===-- Unittests for fmaxl -----------------------------------------------===//
+//
+// 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 "include/math.h"
+#include "src/math/fmaxl.h"
+#include "utils/FPUtil/FPBits.h"
+#include "utils/UnitTest/Test.h"
+
+using FPBits = __llvm_libc::fputil::FPBits<long double>;
+
+long double nan = FPBits::buildNaN(1);
+long double inf = FPBits::inf();
+long double negInf = FPBits::negInf();
+
+TEST(FmaxlTest, NaNArg) {
+  EXPECT_EQ(inf, __llvm_libc::fmaxl(nan, inf));
+  EXPECT_EQ(negInf, __llvm_libc::fmaxl(negInf, nan));
+  EXPECT_EQ(0.0L, __llvm_libc::fmaxl(nan, 0.0L));
+  EXPECT_EQ(-0.0L, __llvm_libc::fmaxl(-0.0L, nan));
+  EXPECT_EQ(-1.2345L, __llvm_libc::fmaxl(nan, -1.2345L));
+  EXPECT_EQ(1.2345L, __llvm_libc::fmaxl(1.2345L, nan));
+  EXPECT_NE(isnan(__llvm_libc::fmaxl(nan, nan)), 0);
+}
+
+TEST(FmaxlTest, InfArg) {
+  EXPECT_EQ(inf, __llvm_libc::fmaxl(negInf, inf));
+  EXPECT_EQ(inf, __llvm_libc::fmaxl(inf, 0.0L));
+  EXPECT_EQ(inf, __llvm_libc::fmaxl(-0.0L, inf));
+  EXPECT_EQ(inf, __llvm_libc::fmaxl(inf, 1.2345L));
+  EXPECT_EQ(inf, __llvm_libc::fmaxl(-1.2345L, inf));
+}
+
+TEST(FmaxlTest, NegInfArg) {
+  EXPECT_EQ(inf, __llvm_libc::fmaxl(inf, negInf));
+  EXPECT_EQ(0.0L, __llvm_libc::fmaxl(negInf, 0.0L));
+  EXPECT_EQ(-0.0L, __llvm_libc::fmaxl(-0.0L, negInf));
+  EXPECT_EQ(-1.2345L, __llvm_libc::fmaxl(negInf, -1.2345L));
+  EXPECT_EQ(1.2345L, __llvm_libc::fmaxl(1.2345L, negInf));
+}
+
+TEST(FmaxlTest, BothZero) {
+  EXPECT_EQ(0.0L, __llvm_libc::fmaxl(0.0L, 0.0L));
+  EXPECT_EQ(0.0L, __llvm_libc::fmaxl(-0.0L, 0.0L));
+  EXPECT_EQ(0.0L, __llvm_libc::fmaxl(0.0L, -0.0L));
+  EXPECT_EQ(-0.0L, __llvm_libc::fmaxl(-0.0L, -0.0L));
+}
+
+TEST(FmaxlTest, InLongDoubleRange) {
+  using UIntType = FPBits::UIntType;
+  constexpr UIntType count = 10000001;
+  constexpr UIntType step = UIntType(-1) / count;
+  for (UIntType i = 0, v = 0, w = UIntType(-1); i <= count;
+       ++i, v += step, w -= step) {
+    long double x = FPBits(v), y = FPBits(w);
+    if (isnan(x) || isinf(x))
+      continue;
+    if (isnan(y) || isinf(y))
+      continue;
+    if ((x == 0) && (y == 0))
+      continue;
+
+    if (x > y) {
+      ASSERT_EQ(x, __llvm_libc::fmaxl(x, y));
+    } else {
+      ASSERT_EQ(y, __llvm_libc::fmaxl(x, y));
+    }
+  }
+}
diff --git a/libc/utils/FPUtil/BasicOperations.h b/libc/utils/FPUtil/BasicOperations.h
@@ -43,6 +43,25 @@ static inline T fmin(T x, T y) {
   }
 }
 
+template <typename T,
+          cpp::EnableIfType<cpp::IsFloatingPointType<T>::Value, int> = 0>
+static inline T fmax(T x, T y) {
+  FPBits<T> bitx(x), bity(y);
+
+  if (bitx.isNaN()) {
+    return y;
+  } else if (bity.isNaN()) {
+    return x;
+  } else if (bitx.sign != bity.sign) {
+    // To make sure that fmax(+0, -0) == +0 == fmax(-0, +0), whenever x and
+    // y has different signs and both are not NaNs, we return the number
+    // with positive sign.
+    return (bitx.sign ? y : x);
+  } else {
+    return (x > y ? x : y);
+  }
+}
+
 } // namespace fputil
 } // namespace __llvm_libc