diff --git a/llvm/lib/Support/Unix/Program.inc b/llvm/lib/Support/Unix/Program.inc
--- a/llvm/lib/Support/Unix/Program.inc
+++ b/llvm/lib/Support/Unix/Program.inc
@@ -329,6 +329,15 @@
   return true;
 }
 
+#if defined(_AIX) && !defined(wait4)
+extern pid_t kwaitpid(int *stat_loc, pid_t pid, int options,
+                      struct rusage *ru_loc, siginfo_t *infop);
+static pid_t wait4(pid_t pid, int *status, int options,
+                   struct rusage *usage) {
+  return kwaitpid(status, pid, options, usage, NULL);
+}
+#endif
+
 namespace llvm {
 
 ProcessInfo sys::Wait(const ProcessInfo &PI, unsigned SecondsToWait,