diff --git a/libc/bionic/bionic_futex.cpp b/libc/bionic/bionic_futex.cpp
new file mode 100644
index 0000000..dd66e40
--- /dev/null
+++ b/libc/bionic/bionic_futex.cpp
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "private/bionic_futex.h"
+
+#include <time.h>
+
+#include "private/bionic_time_conversions.h"
+
+int __futex_wait_ex(volatile void* ftx, bool shared, int value, bool use_realtime_clock,
+                    const timespec* abs_timeout) {
+  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.
+  //
+  // What users really intend is to use CLOCK_MONOTONIC, however only pthread_cond_timedwait()
+  // provides this as an option and even there, a large amount of existing code does not opt into
+  // CLOCK_MONOTONIC.
+  //
+  // 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) {
+      return -ETIMEDOUT;
+    }
+    futex_abs_timeout = &converted_monotonic_abs_timeout;
+  }
+
+  return __futex(ftx, (shared ? FUTEX_WAIT_BITSET : FUTEX_WAIT_BITSET_PRIVATE), value,
+                 futex_abs_timeout, FUTEX_BITSET_MATCH_ANY);
+}