diff --git a/arch/um/include/kern_util.h b/arch/um/include/kern_util.h
index 7a64190c1e53d42e07a98b1f427fd3e23b845aad..b98bdd8e052a5559993ff134eab1a5aedc467889 100644
--- a/arch/um/include/kern_util.h
+++ b/arch/um/include/kern_util.h
@@ -72,7 +72,6 @@ extern void init_flush_vm(void);
 extern void *syscall_sp(void *t);
 extern void syscall_trace(union uml_pt_regs *regs, int entryexit);
 extern int hz(void);
-extern void uml_idle_timer(void);
 extern unsigned int do_IRQ(int irq, union uml_pt_regs *regs);
 extern int external_pid(void *t);
 extern void interrupt_end(void);
diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index 31fb3235f55205beebaca4c84ec0a55426e1e75b..4ae73c0e54850c4068e1ddf0cf9afc33f6e96239 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -66,6 +66,7 @@ void switch_timers(int to_real)
 		       errno);
 }
 
+#ifdef UML_CONFIG_MODE_TT
 void uml_idle_timer(void)
 {
 	if(signal(SIGVTALRM, SIG_IGN) == SIG_ERR)
@@ -75,6 +76,7 @@ void uml_idle_timer(void)
 		    SA_RESTART, SIGUSR1, SIGIO, SIGWINCH, SIGVTALRM, -1);
 	set_interval(ITIMER_REAL);
 }
+#endif
 
 unsigned long long os_nsecs(void)
 {