diff --git a/libc/bionic/bionic_arc4random.cpp b/libc/bionic/bionic_arc4random.cpp
new file mode 100644
index 0000000..d20cb68
--- /dev/null
+++ b/libc/bionic/bionic_arc4random.cpp
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2016 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_arc4random.h"
+
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/auxv.h>
+#include <syscall.h>
+#include <unistd.h>
+
+#include "private/KernelArgumentBlock.h"
+#include "private/libc_logging.h"
+
+void __libc_safe_arc4random_buf(void* buf, size_t n, KernelArgumentBlock& args) {
+  static bool have_getrandom = syscall(SYS_getrandom, nullptr, 0, 0) == -1 && errno != ENOSYS;
+  static bool have_urandom = access("/dev/urandom", R_OK) == 0;
+  static size_t at_random_bytes_consumed = 0;
+
+  if (have_getrandom || have_urandom) {
+    arc4random_buf(buf, n);
+    return;
+  }
+
+  if (at_random_bytes_consumed + n > 16) {
+    __libc_fatal("ran out of AT_RANDOM bytes, have %zu, requested %zu",
+                 16 - at_random_bytes_consumed, n);
+  }
+
+  memcpy(buf, reinterpret_cast<char*>(args.getauxval(AT_RANDOM)) + at_random_bytes_consumed, n);
+  at_random_bytes_consumed += n;
+  return;
+}