diff --git a/libc/bionic/bionic_futex.cpp b/libc/bionic/bionic_futex.cpp
index 0ac1f6e..aa8234f 100644
--- a/libc/bionic/bionic_futex.cpp
+++ b/libc/bionic/bionic_futex.cpp
@@ -28,6 +28,7 @@
 
 #include "private/bionic_futex.h"
 
+#include <stdatomic.h>
 #include <time.h>
 
 #include "private/bionic_time_conversions.h"
@@ -35,7 +36,6 @@
 static inline __always_inline int FutexWithTimeout(volatile void* ftx, int op, int value,
                                                    bool use_realtime_clock,
                                                    const timespec* abs_timeout, int bitset) {
-  const timespec* futex_abs_timeout = abs_timeout;
   // pthread's and semaphore's default behavior is to use CLOCK_REALTIME, however this behavior is
   // essentially never intended, as that clock is prone to change discontinuously.
   //
@@ -46,16 +46,26 @@
   // We have seen numerous bugs directly attributable to this difference.  Therefore, we provide
   // this general workaround to always use CLOCK_MONOTONIC for waiting, regardless of what the input
   // timespec is.
-  timespec converted_monotonic_abs_timeout;
-  if (abs_timeout && use_realtime_clock) {
-    monotonic_time_from_realtime_time(converted_monotonic_abs_timeout, *abs_timeout);
-    if (converted_monotonic_abs_timeout.tv_sec < 0) {
+  timespec converted_timeout;
+  if (abs_timeout) {
+    if ((op & FUTEX_CMD_MASK) == FUTEX_LOCK_PI) {
+      if (!use_realtime_clock) {
+        realtime_time_from_monotonic_time(converted_timeout, *abs_timeout);
+        abs_timeout = &converted_timeout;
+      }
+    } else {
+      op &= ~FUTEX_CLOCK_REALTIME;
+      if (use_realtime_clock) {
+        monotonic_time_from_realtime_time(converted_timeout, *abs_timeout);
+        abs_timeout = &converted_timeout;
+      }
+    }
+    if (abs_timeout->tv_sec < 0) {
       return -ETIMEDOUT;
     }
-    futex_abs_timeout = &converted_monotonic_abs_timeout;
   }
 
-  return __futex(ftx, op, value, futex_abs_timeout, bitset);
+  return __futex(ftx, op, value, abs_timeout, bitset);
 }
 
 int __futex_wait_ex(volatile void* ftx, bool shared, int value, bool use_realtime_clock,
@@ -66,6 +76,22 @@
 
 int __futex_pi_lock_ex(volatile void* ftx, bool shared, bool use_realtime_clock,
                        const timespec* abs_timeout) {
-  return FutexWithTimeout(ftx, (shared ? FUTEX_LOCK_PI : FUTEX_LOCK_PI_PRIVATE), 0,
-                          use_realtime_clock, abs_timeout, 0);
+  // We really want FUTEX_LOCK_PI2 which is default CLOCK_MONOTONIC, but that isn't supported
+  // on linux before 5.14.  FUTEX_LOCK_PI uses CLOCK_REALTIME.  Here we verify support.
+
+  static atomic_int lock_op = 0;
+  int op = atomic_load_explicit(&lock_op, memory_order_relaxed);
+  if (op == 0) {
+    uint32_t tmp = 0;
+    if (__futex(&tmp, FUTEX_LOCK_PI2, 0, nullptr, 0) == 0) {
+      __futex(&tmp, FUTEX_UNLOCK_PI, 0, nullptr, 0);
+      op = FUTEX_LOCK_PI2;
+    } else {
+      op = FUTEX_LOCK_PI;
+    }
+    atomic_store_explicit(&lock_op, op, memory_order_relaxed);
+  }
+
+  if (!shared) op |= FUTEX_PRIVATE_FLAG;
+  return FutexWithTimeout(ftx, op, 0 /* value */, use_realtime_clock, abs_timeout, 0 /* bitset */);
 }
diff --git a/libc/bionic/bionic_time_conversions.cpp b/libc/bionic/bionic_time_conversions.cpp
index d21e12e..9f3c50d 100644
--- a/libc/bionic/bionic_time_conversions.cpp
+++ b/libc/bionic/bionic_time_conversions.cpp
@@ -52,23 +52,32 @@
   tv.tv_usec = ts.tv_nsec / 1000;
 }
 
-void monotonic_time_from_realtime_time(timespec& monotonic_time, const timespec& realtime_time) {
-  monotonic_time = realtime_time;
+static void convert_timespec_clocks(timespec& new_time, clockid_t new_clockbase,
+                                    const timespec& old_time, clockid_t old_clockbase) {
+  // get reference clocks
+  timespec new_clock;
+  clock_gettime(new_clockbase, &new_clock);
+  timespec old_clock;
+  clock_gettime(old_clockbase, &old_clock);
 
-  timespec cur_monotonic_time;
-  clock_gettime(CLOCK_MONOTONIC, &cur_monotonic_time);
-  timespec cur_realtime_time;
-  clock_gettime(CLOCK_REALTIME, &cur_realtime_time);
+  // compute new time by moving old delta to the new clock.
+  new_time.tv_sec = old_time.tv_sec - old_clock.tv_sec + new_clock.tv_sec;
+  new_time.tv_nsec = old_time.tv_nsec - old_clock.tv_nsec + new_clock.tv_nsec;
 
-  monotonic_time.tv_nsec -= cur_realtime_time.tv_nsec;
-  monotonic_time.tv_nsec += cur_monotonic_time.tv_nsec;
-  if (monotonic_time.tv_nsec >= NS_PER_S) {
-    monotonic_time.tv_nsec -= NS_PER_S;
-    monotonic_time.tv_sec += 1;
-  } else if (monotonic_time.tv_nsec < 0) {
-    monotonic_time.tv_nsec += NS_PER_S;
-    monotonic_time.tv_sec -= 1;
+  // correct nsec to second wrap.
+  if (new_time.tv_nsec >= NS_PER_S) {
+    new_time.tv_nsec -= NS_PER_S;
+    new_time.tv_sec += 1;
+  } else if (new_time.tv_nsec < 0) {
+    new_time.tv_nsec += NS_PER_S;
+    new_time.tv_sec -= 1;
   }
-  monotonic_time.tv_sec -= cur_realtime_time.tv_sec;
-  monotonic_time.tv_sec += cur_monotonic_time.tv_sec;
+}
+
+void monotonic_time_from_realtime_time(timespec& monotonic_time, const timespec& realtime_time) {
+  convert_timespec_clocks(monotonic_time, CLOCK_MONOTONIC, realtime_time, CLOCK_REALTIME);
+}
+
+void realtime_time_from_monotonic_time(timespec& realtime_time, const timespec& monotonic_time) {
+  convert_timespec_clocks(realtime_time, CLOCK_REALTIME, monotonic_time, CLOCK_MONOTONIC);
 }
diff --git a/libc/private/bionic_constants.h b/libc/private/bionic_constants.h
index 05914f4..6274fe2 100644
--- a/libc/private/bionic_constants.h
+++ b/libc/private/bionic_constants.h
@@ -16,7 +16,7 @@
 
 #pragma once
 
-#define NS_PER_S 1000000000
+#define NS_PER_S 1'000'000'000LL
 
 // Size of the shadow call stack. This can be small because these stacks only
 // contain return addresses. This must be a power of 2 so the mask trick works.
diff --git a/libc/private/bionic_time_conversions.h b/libc/private/bionic_time_conversions.h
index fb049f2..c6b3c78 100644
--- a/libc/private/bionic_time_conversions.h
+++ b/libc/private/bionic_time_conversions.h
@@ -45,6 +45,9 @@
 __LIBC_HIDDEN__ void monotonic_time_from_realtime_time(timespec& monotonic_time,
                                                        const timespec& realtime_time);
 
+__LIBC_HIDDEN__ void realtime_time_from_monotonic_time(timespec& realtime_time,
+                                                       const timespec& monotonic_time);
+
 __END_DECLS
 
 static inline int check_timespec(const timespec* ts, bool null_allowed) {