diff --git a/arch/s390/kernel/runtime_instr.c b/arch/s390/kernel/runtime_instr.c
index 09f5bf0d5c0c..125c7f6e8715 100644
--- a/arch/s390/kernel/runtime_instr.c
+++ b/arch/s390/kernel/runtime_instr.c
@@ -18,6 +18,8 @@
 #include <asm/cpu_mf.h>
 #include <asm/irq.h>
 
+#include "entry.h"
+
 /* empty control block to disable RI by loading it */
 struct runtime_instr_cb runtime_instr_empty_cb;
 
@@ -59,7 +61,13 @@ static void init_runtime_instr_cb(struct runtime_instr_cb *cb)
 	cb->v = 1;
 }
 
-SYSCALL_DEFINE1(s390_runtime_instr, int, command)
+/*
+ * The signum argument is unused. In older kernels it was used to
+ * specify a real-time signal. For backwards compatibility user space
+ * should pass a valid real-time signal number (the signum argument
+ * was checked in older kernels).
+ */
+SYSCALL_DEFINE2(s390_runtime_instr, int, command, int, signum)
 {
 	struct runtime_instr_cb *cb;