diff --git a/sys/x86/isa/atrtc.c b/sys/x86/isa/atrtc.c
index 45fd00c64da2..7c42cc28566e 100644
--- a/sys/x86/isa/atrtc.c
+++ b/sys/x86/isa/atrtc.c
@@ -42,6 +42,7 @@
 #include <sys/module.h>
 #include <sys/proc.h>
 #include <sys/rman.h>
+#include <sys/sysctl.h>
 #include <sys/timeet.h>
 
 #include <isa/rtc.h>