diff --git a/libc/src/time/time_zone_posix.h b/libc/src/time/time_zone_posix.h
--- a/libc/src/time/time_zone_posix.h
+++ b/libc/src/time/time_zone_posix.h
@@ -11,8 +11,8 @@
 
 #include <stdint.h> // int8_t, int16_t and int32_t
 
-#include "src/__support/CPP/Optional.h"
 #include "src/__support/CPP/StringView.h"
+#include "src/__support/CPP/optional.h"
 
 #include <stdint.h> // int8_t, int16_t and int32_t
 
@@ -91,7 +91,7 @@
   // filling in any missing values (DST offset, or start/end transition times)
   // with the standard-defined defaults. Returns false if the specification
   // could not be parsed (although some fields of *res may have been altered).
-  static cpp::Optional<PosixTimeZone>
+  static cpp::optional<PosixTimeZone>
   ParsePosixSpec(const cpp::StringView spec);
 
   cpp::StringView m_spec;
@@ -114,13 +114,13 @@
   bool UpdateDstEnd();
   bool SpecHasData();
 
-  cpp::Optional<int> ParseInt(int min, int max);
-  cpp::Optional<cpp::StringView> ParseAbbr();
-  cpp::Optional<int32_t> ParseOffset(int min_hour, int max_hour, int sign);
-  cpp::Optional<PosixTransition> ParseMonthWeekWeekday();
-  cpp::Optional<PosixTransition> ParseNonLeapDay();
-  cpp::Optional<PosixTransition> ParseLeapDay();
-  cpp::Optional<PosixTransition> ParseDateTime();
+  cpp::optional<int> ParseInt(int min, int max);
+  cpp::optional<cpp::StringView> ParseAbbr();
+  cpp::optional<int32_t> ParseOffset(int min_hour, int max_hour, int sign);
+  cpp::optional<PosixTransition> ParseMonthWeekWeekday();
+  cpp::optional<PosixTransition> ParseNonLeapDay();
+  cpp::optional<PosixTransition> ParseLeapDay();
+  cpp::optional<PosixTransition> ParseDateTime();
 };
 
 } // namespace time_zone_posix
diff --git a/libc/src/time/time_zone_posix.cpp b/libc/src/time/time_zone_posix.cpp
--- a/libc/src/time/time_zone_posix.cpp
+++ b/libc/src/time/time_zone_posix.cpp
@@ -14,14 +14,14 @@
 // required unsigned values from 0 through 24.
 static constexpr int MAX_HOURS_IN_TRANSITION_TIMES = 167;
 
-cpp::Optional<int> PosixTimeZone::ParseInt(int min, int max) {
+cpp::optional<int> PosixTimeZone::ParseInt(int min, int max) {
   if (m_spec.size() == 0)
-    return cpp::Nullopt;
+    return cpp::nullopt;
 
   char *pEnd;
   int value = strtol(m_spec.data(), &pEnd, 10); // NOLINT(runtime/deprecated_fn)
   if (value < min || value > max)
-    return cpp::Nullopt;
+    return cpp::nullopt;
 
   // Delete the number from the input string.
   size_t len = pEnd - m_spec.data();
@@ -30,17 +30,17 @@
 }
 
 // abbr = <.*?> | [^-+,\d]{3,}
-cpp::Optional<cpp::StringView> PosixTimeZone::ParseAbbr() {
+cpp::optional<cpp::StringView> PosixTimeZone::ParseAbbr() {
   if (m_spec.size() == 0)
-    return cpp::Nullopt;
+    return cpp::nullopt;
 
   // Handle special zoneinfo <...> form.
-  cpp::Optional<cpp::StringView> abbr;
+  cpp::optional<cpp::StringView> abbr;
   if (m_spec.starts_with('<')) {
     m_spec.remove_prefix(1);
     const auto pos = m_spec.find_first_of('>');
     if (pos == cpp::StringView::npos)
-      return cpp::Nullopt;
+      return cpp::nullopt;
     abbr = m_spec.substr(0, pos);
     // Delete the data up to and including '>' character.
     m_spec.remove_prefix(pos + 1);
@@ -57,17 +57,17 @@
     len++;
   }
   if (len < 3)
-    return cpp::Nullopt;
+    return cpp::nullopt;
   abbr = m_spec.substr(0, len);
   m_spec.remove_prefix(len);
   return abbr;
 }
 
 // offset = [+|-]hh[:mm[:ss]] (aggregated into single seconds value)
-cpp::Optional<int32_t> PosixTimeZone::ParseOffset(int min_hour, int max_hour,
+cpp::optional<int32_t> PosixTimeZone::ParseOffset(int min_hour, int max_hour,
                                                   int sign) {
   if (m_spec.size() == 0)
-    return cpp::Nullopt;
+    return cpp::nullopt;
 
   // Handle [+|-].
   if (m_spec.starts_with('+') || m_spec.starts_with('-')) {
@@ -81,9 +81,9 @@
   int seconds = 0;
 
   // Parse hours - hh
-  cpp::Optional<int> result = ParseInt(min_hour, max_hour);
+  cpp::optional<int> result = ParseInt(min_hour, max_hour);
   if (!result.has_value())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   hours = result.value();
 
   // Check for optional minutes.
@@ -94,7 +94,7 @@
     // Parse minutes.
     result = ParseInt(0, 59);
     if (!result.has_value())
-      return cpp::Nullopt;
+      return cpp::nullopt;
     minutes = result.value();
 
     // Check for optional seconds.
@@ -105,7 +105,7 @@
       // Parse seconds.
       result = ParseInt(0, 59);
       if (!result.has_value())
-        return cpp::Nullopt;
+        return cpp::nullopt;
       seconds = result.value();
     }
   }
@@ -115,41 +115,41 @@
 
 // (M) the Nth weekday of a month (e.g., the 2nd Sunday in March).
 // Mm.w.d
-cpp::Optional<PosixTransition> PosixTimeZone::ParseMonthWeekWeekday() {
+cpp::optional<PosixTransition> PosixTimeZone::ParseMonthWeekWeekday() {
   // Parse month.
-  cpp::Optional<int> result = ParseInt(1, 12);
+  cpp::optional<int> result = ParseInt(1, 12);
   if (!result.has_value())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   int month = result.value();
 
   // Error if there is no dot.
   if (!m_spec.starts_with('.'))
-    return cpp::Nullopt;
+    return cpp::nullopt;
   m_spec.remove_prefix(1);
 
   // Error if there is no week.
   if (m_spec.size() == 0)
-    return cpp::Nullopt;
+    return cpp::nullopt;
 
   // Parse week.
   result = ParseInt(1, 5);
   if (!result.has_value())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   int week = result.value();
 
   // Error if there is no dot.
   if (!m_spec.starts_with('.'))
-    return cpp::Nullopt;
+    return cpp::nullopt;
   m_spec.remove_prefix(1);
 
   // Error if there is no weekday.
   if (m_spec.size() == 0)
-    return cpp::Nullopt;
+    return cpp::nullopt;
 
   // Parse Weekday.
   result = ParseInt(0, 6);
   if (!result.has_value())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   int weekday = result.value();
 
   PosixTransition posixTransition;
@@ -162,10 +162,10 @@
 
 // Parse Jn
 // (J) the Nth day of the year (1 <= N <= 365), excluding leap days.
-cpp::Optional<PosixTransition> PosixTimeZone::ParseNonLeapDay() {
-  const cpp::Optional<int> result = ParseInt(1, 365);
+cpp::optional<PosixTransition> PosixTimeZone::ParseNonLeapDay() {
+  const cpp::optional<int> result = ParseInt(1, 365);
   if (!result.has_value())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   PosixTransition posixTransition;
   posixTransition.date.fmt = PosixTransition::J;
   posixTransition.date.j.day = static_cast<int16_t>(result.value());
@@ -174,10 +174,10 @@
 
 // Parse n
 // (N) the Nth day of the year (0 <= N <= 365), including leap days
-cpp::Optional<PosixTransition> PosixTimeZone::ParseLeapDay() {
-  const cpp::Optional<int> result = ParseInt(0, 365);
+cpp::optional<PosixTransition> PosixTimeZone::ParseLeapDay() {
+  const cpp::optional<int> result = ParseInt(0, 365);
   if (!result.has_value())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   PosixTransition posixTransition;
   posixTransition.date.fmt = PosixTransition::N;
   posixTransition.date.n.day = static_cast<int16_t>(result.value());
@@ -185,12 +185,12 @@
 }
 
 // datetime = ( Jn | n | Mm.w.d ) [ / offset ]
-cpp::Optional<PosixTransition> PosixTimeZone::ParseDateTime() {
+cpp::optional<PosixTransition> PosixTimeZone::ParseDateTime() {
   PosixTransition posixTransition;
   if (m_spec.starts_with(',')) {
     m_spec.remove_prefix(1);
 
-    cpp::Optional<PosixTransition> optionalPosixTransition;
+    cpp::optional<PosixTransition> optionalPosixTransition;
     if (m_spec.starts_with('M')) {
       m_spec.remove_prefix(1);
       optionalPosixTransition = ParseMonthWeekWeekday(); // Mm.w.d
@@ -208,10 +208,10 @@
   posixTransition.time.offset = 2 * 60 * 60; // default offset is 02:00:00
   if (m_spec.starts_with('/')) {
     m_spec.remove_prefix(1);
-    const cpp::Optional<int32_t> offset = ParseOffset(
+    const cpp::optional<int32_t> offset = ParseOffset(
         -MAX_HOURS_IN_TRANSITION_TIMES, MAX_HOURS_IN_TRANSITION_TIMES, 1);
     if (!offset.has_value())
-      return cpp::Nullopt;
+      return cpp::nullopt;
     posixTransition.time.offset = offset.value();
   }
   return posixTransition;
@@ -234,7 +234,7 @@
 }
 
 bool PosixTimeZone::UpdateStdOffset() {
-  const cpp::Optional<int32_t> offset = ParseOffset(0, 24, -1);
+  const cpp::optional<int32_t> offset = ParseOffset(0, 24, -1);
   if (!offset.has_value())
     return false;
   m_std_offset = offset.value();
@@ -244,7 +244,7 @@
 bool PosixTimeZone::UpdateDstOffset() {
   m_dst_offset = m_std_offset + (60 * 60); // default
   if (!m_spec.starts_with(',')) {
-    const cpp::Optional<int32_t> offset = ParseOffset(0, 24, -1);
+    const cpp::optional<int32_t> offset = ParseOffset(0, 24, -1);
     if (!offset.has_value())
       return false;
     m_dst_offset = offset.value();
@@ -275,28 +275,28 @@
 }
 
 // spec = std offset [ dst [ offset ] , datetime , datetime ]
-cpp::Optional<PosixTimeZone>
+cpp::optional<PosixTimeZone>
 PosixTimeZone::ParsePosixSpec(const cpp::StringView spec) {
   if (spec.starts_with(':'))
-    return cpp::Nullopt;
+    return cpp::nullopt;
 
   PosixTimeZone res(spec);
   if (!res.UpdateStdAbbr())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   if (!res.UpdateStdOffset())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   if (res.m_spec.size() == 0)
     return res;
   if (!res.UpdateDstAbbr())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   if (!res.UpdateDstOffset())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   if (!res.UpdateDstStart())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   if (!res.UpdateDstEnd())
-    return cpp::Nullopt;
+    return cpp::nullopt;
   if (res.m_spec.size() != 0)
-    return cpp::Nullopt;
+    return cpp::nullopt;
   return res;
 }
 
diff --git a/libc/test/src/time/time_zone_posix_test.cpp b/libc/test/src/time/time_zone_posix_test.cpp
--- a/libc/test/src/time/time_zone_posix_test.cpp
+++ b/libc/test/src/time/time_zone_posix_test.cpp
@@ -247,7 +247,7 @@
 TEST(LlvmLibcParsePosixSpec, ValidTestAndVerify) {
   __llvm_libc::cpp::StringView timezone_spec("PST8PDT,M3.2.0,M11.1.0");
   // TODO(rtenneti): Use a special matcher to verify the data.
-  __llvm_libc::cpp::Optional<__llvm_libc::time_zone_posix::PosixTimeZone>
+  __llvm_libc::cpp::optional<__llvm_libc::time_zone_posix::PosixTimeZone>
       posix_result =
           __llvm_libc::time_zone_posix::PosixTimeZone::ParsePosixSpec(
               timezone_spec);