diff --git a/winsup/cygwin/exceptions.cc b/winsup/cygwin/exceptions.cc
index 3195d5719..60c1f594f 100644
--- a/winsup/cygwin/exceptions.cc
+++ b/winsup/cygwin/exceptions.cc
@@ -1527,11 +1527,14 @@ sigpacket::process ()
   if ((HANDLE) *tls)
     tls->signal_debugger (si);
 
-  if (issig_wait)
+  tls->lock ();
+  if (issig_wait && tls->sigwait_mask != 0)
     {
       tls->sigwait_mask = 0;
+      tls->unlock ();
       goto dosig;
     }
+  tls->unlock ();
 
   if (handler == SIG_IGN)
     {
diff --git a/winsup/cygwin/release/3.5.5 b/winsup/cygwin/release/3.5.5
index b70b91ed8..d91f2b92c 100644
--- a/winsup/cygwin/release/3.5.5
+++ b/winsup/cygwin/release/3.5.5
@@ -42,3 +42,6 @@ Fixes:
 
 - Fix NtCreateEvent() error in create_lock_ob() called from flock().
   Addresses: https://cygwin.com/pipermail/cygwin/2024-November/256750.html
+
+- Fix segfault in sigtimedwait() when using timeout.
+  Addresses: https://cygwin.com/pipermail/cygwin/2024-November/256762.html
diff --git a/winsup/cygwin/signal.cc b/winsup/cygwin/signal.cc
index 77152910b..9ee6cf995 100644
--- a/winsup/cygwin/signal.cc
+++ b/winsup/cygwin/signal.cc
@@ -615,6 +615,7 @@ sigwait_common (const sigset_t *set, siginfo_t *info, PLARGE_INTEGER waittime)
       set_signal_mask (_my_tls.sigwait_mask, *set);
       sig_dispatch_pending (true);
 
+do_wait:
       switch (cygwait (NULL, waittime,
 		       cw_sig_eintr | cw_cancel | cw_cancel_self))
 	{
@@ -640,6 +641,17 @@ sigwait_common (const sigset_t *set, siginfo_t *info, PLARGE_INTEGER waittime)
 	    }
 	  break;
 	case WAIT_TIMEOUT:
+	  _my_tls.lock ();
+	  if (_my_tls.sigwait_mask == 0)
+	    {
+	      /* sigpacket::process() already started.
+	         Will surely be signalled soon. */
+	      waittime = cw_infinite;
+	      _my_tls.unlock ();
+	      goto do_wait;
+	    }
+	  _my_tls.sigwait_mask = 0;
+	  _my_tls.unlock ();
 	  set_errno (EAGAIN);
 	  break;
 	default: