diff --git a/src/header/time/mod.rs b/src/header/time/mod.rs
index fd0ba15035..b534dc5274 100644
--- a/src/header/time/mod.rs
+++ b/src/header/time/mod.rs
@@ -66,6 +66,9 @@ pub(crate) struct timer_internal_t {
     pub caller_thread: crate::pthread::OsTid,
     // relibc handles it_interval, not the kernel
     pub next_wake_time: itimerspec,
+    // When non-zero, timer_routine delivers SIGALRM via kill(process_pid, sig)
+    // instead of rlct_kill (thread-specific). Used by alarm().
+    pub process_pid: platform::types::pid_t,
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/time.h.html>.
diff --git a/src/header/unistd/mod.rs b/src/header/unistd/mod.rs
index aa31284d81..c4d5f17b00 100644
--- a/src/header/unistd/mod.rs
+++ b/src/header/unistd/mod.rs
@@ -24,7 +24,7 @@ use crate::{
     },
     out::Out,
     platform::{
-        self, ERRNO, Pal, Sys,
+        self, ERRNO, Pal, PalSignal, Sys,
         types::{
             c_char, c_int, c_long, c_short, c_uint, c_ulonglong, c_void, gid_t, off_t, pid_t,
             size_t, ssize_t, suseconds_t, time_t, uid_t, useconds_t,
@@ -137,28 +137,7 @@ pub unsafe extern "C" fn access(path: *const c_char, mode: c_int) -> c_int {
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/alarm.html>.
 #[unsafe(no_mangle)]
 pub extern "C" fn alarm(seconds: c_uint) -> c_uint {
-    // TODO setitimer is unimplemented on Redox and obsolete
-    let timer = sys_time::itimerval {
-        it_value: timeval {
-            tv_sec: time_t::from(seconds),
-            tv_usec: 0,
-        },
-        ..Default::default()
-    };
-    let mut otimer = sys_time::itimerval::default();
-
-    let errno_backup = platform::ERRNO.get();
-    let secs =
-        if unsafe { sys_time::setitimer(sys_time::ITIMER_REAL, &raw const timer, &raw mut otimer) }
-            < 0
-        {
-            0
-        } else {
-            otimer.it_value.tv_sec as c_uint + if otimer.it_value.tv_usec > 0 { 1 } else { 0 }
-        };
-    platform::ERRNO.set(errno_backup);
-
-    secs
+    Sys::alarm(seconds)
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/chdir.html>.
diff --git a/src/platform/pal/signal.rs b/src/platform/pal/signal.rs
index 52670daa6f..b8ed26acea 100644
--- a/src/platform/pal/signal.rs
+++ b/src/platform/pal/signal.rs
@@ -4,8 +4,9 @@ use crate::{
     header::{
         bits_time::timespec,
         signal::{sigaction, siginfo_t, sigset_t, sigval, stack_t},
-        sys_time::itimerval,
+        sys_time::{self, itimerval},
     },
+    platform,
 };
 
 pub trait PalSignal: Pal {
@@ -21,6 +22,32 @@ pub trait PalSignal: Pal {
 
     fn setitimer(which: c_int, new: &itimerval, old: Option<&mut itimerval>) -> Result<()>;
 
+    /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/alarm.html>.
+    ///
+    /// Default implementation uses setitimer(ITIMER_REAL). Platforms that do not
+    /// support setitimer (e.g. Redox) must override this.
+    fn alarm(seconds: c_uint) -> c_uint {
+        use crate::header::sys_select::timeval;
+
+        let timer = itimerval {
+            it_value: timeval {
+                tv_sec: time_t::from(seconds),
+                tv_usec: 0,
+            },
+            ..Default::default()
+        };
+        let mut otimer = itimerval::default();
+
+        let errno_backup = platform::ERRNO.get();
+        let secs = if Self::setitimer(sys_time::ITIMER_REAL, &timer, Some(&mut otimer)).is_err() {
+            0
+        } else {
+            otimer.it_value.tv_sec as c_uint + if otimer.it_value.tv_usec > 0 { 1 } else { 0 }
+        };
+        platform::ERRNO.set(errno_backup);
+        secs
+    }
+
     fn sigaction(sig: c_int, act: Option<&sigaction>, oact: Option<&mut sigaction>) -> Result<()>;
 
     unsafe fn sigaltstack(ss: Option<&stack_t>, old_ss: Option<&mut stack_t>) -> Result<()>;
diff --git a/tests/Makefile.tests.mk b/tests/Makefile.tests.mk
index 1f591dabc2..7ace459d3a 100644
--- a/tests/Makefile.tests.mk
+++ b/tests/Makefile.tests.mk
@@ -159,6 +159,7 @@ EXPECT_NAMES=\
 	time/timegm \
 	time/tzset \
 	unistd/access \
+	unistd/alarm \
 	unistd/constants \
 	unistd/confstr \
 	unistd/dup \