diff --git a/qse/lib/si/aio-pro.c b/qse/lib/si/aio-pro.c
index 23794a9d..db141065 100644
--- a/qse/lib/si/aio-pro.c
+++ b/qse/lib/si/aio-pro.c
@@ -33,6 +33,7 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <sys/wait.h>
+#include <signal.h>
 
 /* ========================================================================= */