diff --git a/libc/bionic/ndk_cruft.cpp b/libc/bionic/ndk_cruft.cpp
index 295418b..46cc1f0 100644
--- a/libc/bionic/ndk_cruft.cpp
+++ b/libc/bionic/ndk_cruft.cpp
@@ -31,10 +31,12 @@
 
 #include <ctype.h>
 #include <inttypes.h>
+#include <linux/futex.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/resource.h>
+#include <sys/syscall.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <sys/wait.h>
@@ -199,4 +201,25 @@
   return vdprintf(fd, fmt, ap);
 }
 
+static inline int __futex(volatile void* ftx, int op, int value, const struct timespec* timeout) {
+  // Our generated syscall assembler sets errno, but our callers (pthread functions) don't want to.
+  int saved_errno = errno;
+  if (syscall(__NR_futex, ftx, op, value, timeout) == 0) {
+    return 0;
+  }
+  int result = -errno;
+  errno = saved_errno;
+  return result;
+}
+
+// This used to be in <sys/atomics.h>.
+extern "C" int __futex_wake(volatile void* ftx, int count) {
+  return __futex(ftx, FUTEX_WAKE, count, NULL);
+}
+
+// This used to be in <sys/atomics.h>.
+extern "C" int __futex_wait(volatile void* ftx, int value, const struct timespec* timeout) {
+  return __futex(ftx, FUTEX_WAIT, value, timeout);
+}
+
 #endif