diff --git a/ProcessUNIX.c b/ProcessUNIX.c
index be169d1fb2307fd6cf5c5f5d5c134e152838bb44..6f187bb8feaeeba8e29cc39391d38d881c8adac3 100644
--- a/ProcessUNIX.c
+++ b/ProcessUNIX.c
@@ -1906,7 +1906,7 @@ static pid_t kwsysProcessFork(kwsysProcess* cp,
 #if defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__)
 # define KWSYSPE_PS_COMMAND "ps axo pid,ppid"
 # define KWSYSPE_PS_FORMAT  "%d %d\n"
-#elif defined(__hpux) || defined(__sparc) || defined(__sgi)
+#elif defined(__hpux) || defined(__sparc) || defined(__sgi) || defined(_AIX)
 # define KWSYSPE_PS_COMMAND "ps -ef"
 # define KWSYSPE_PS_FORMAT  "%*s %d %d %*[^\n]\n"
 #endif