diff --git a/lib/libthr/thread/thr_cancel.c b/lib/libthr/thread/thr_cancel.c
--- a/lib/libthr/thread/thr_cancel.c
+++ b/lib/libthr/thread/thr_cancel.c
@@ -83,25 +83,25 @@
 _thr_setcancelstate(int state, int *oldstate)
 {
 	struct pthread *curthread = _get_curthread();
-	int oldval;
+	int oldval, val;
 
-	oldval = curthread->cancel_enable;
 	switch (state) {
 	case PTHREAD_CANCEL_DISABLE:
-		curthread->cancel_enable = 0;
+		val = 0;
 		break;
 	case PTHREAD_CANCEL_ENABLE:
-		curthread->cancel_enable = 1;
-		if (curthread->cancel_async)
-			testcancel(curthread);
+		val = 1;
 		break;
 	default:
 		return (EINVAL);
 	}
 
-	if (oldstate) {
+	oldval = atomic_swap_int(&curthread->cancel_enable, val);
+	if (state == PTHREAD_CANCEL_ENABLE && curthread->cancel_async)
+		testcancel(curthread);
+	if (oldstate != NULL) {
 		*oldstate = oldval ? PTHREAD_CANCEL_ENABLE :
-			PTHREAD_CANCEL_DISABLE;
+		    PTHREAD_CANCEL_DISABLE;
 	}
 	return (0);
 }
@@ -125,9 +125,9 @@
 		return (EINVAL);
 	}
 
-	if (oldtype) {
+	if (oldtype != NULL) {
 		*oldtype = oldval ? PTHREAD_CANCEL_ASYNCHRONOUS :
-		 	PTHREAD_CANCEL_DEFERRED;
+		    PTHREAD_CANCEL_DEFERRED;
 	}
 	return (0);
 }
@@ -166,9 +166,8 @@
 _thr_cancel_leave(struct pthread *curthread, int maycancel)
 {
 	curthread->cancel_point = 0;
-	if (__predict_false(SHOULD_CANCEL(curthread) &&
-	    !THR_IN_CRITICAL(curthread) && maycancel))
-		_pthread_exit(PTHREAD_CANCELED);
+	if (maycancel)
+		testcancel(curthread);
 }
 
 void
diff --git a/lib/libthr/thread/thr_private.h b/lib/libthr/thread/thr_private.h
--- a/lib/libthr/thread/thr_private.h
+++ b/lib/libthr/thread/thr_private.h
@@ -562,8 +562,12 @@
 
 	/* Deferred threads from pthread_cond_signal. */
 	unsigned int 		*defer_waiters[MAX_DEFER_WAITERS];
-#define _pthread_endzero	wake_addr
 
+	/* rtld thread-local dlerror message and seen control */
+	char			dlerror_msg[512];
+	int			dlerror_seen;
+
+#define _pthread_endzero	wake_addr
 	struct wake_addr	*wake_addr;
 #define WAKE_ADDR(td)           ((td)->wake_addr)
 
@@ -572,10 +576,6 @@
 
 	/* pthread_set/get_name_np */
 	char			*name;
-
-	/* rtld thread-local dlerror message and seen control */
-	char			dlerror_msg[512];
-	int			dlerror_seen;
 };
 
 #define THR_SHOULD_GC(thrd) 						\
diff --git a/lib/libthr/thread/thr_sig.c b/lib/libthr/thread/thr_sig.c
--- a/lib/libthr/thread/thr_sig.c
+++ b/lib/libthr/thread/thr_sig.c
@@ -185,8 +185,7 @@
 }
 
 static void
-sigcancel_handler(int sig __unused,
-	siginfo_t *info __unused, ucontext_t *ucp)
+sigcancel_handler(int sig __unused, siginfo_t *info __unused, ucontext_t *ucp)
 {
 	struct pthread *curthread = _get_curthread();
 	int err;
@@ -354,9 +353,11 @@
 	 *    on getting a signal before it agrees to return.
  	 */
 	if (curthread->cancel_point) {
-		if (curthread->in_sigsuspend && ucp) {
-			SIGADDSET(ucp->uc_sigmask, SIGCANCEL);
-			curthread->unblock_sigcancel = 1;
+		if (curthread->in_sigsuspend) {
+			if (ucp != NULL) {
+				SIGADDSET(ucp->uc_sigmask, SIGCANCEL);
+				curthread->unblock_sigcancel = 1;
+			}
 			_thr_send_sig(curthread, SIGCANCEL);
 		} else
 			thr_wake(curthread->tid);
@@ -365,8 +366,8 @@
 		 * asynchronous cancellation mode, act upon
 		 * immediately.
 		 */
-		_pthread_exit_mask(PTHREAD_CANCELED,
-		    ucp? &ucp->uc_sigmask : NULL);
+		_pthread_exit_mask(PTHREAD_CANCELED, ucp != NULL ?
+		    &ucp->uc_sigmask : NULL);
 	}
 }
 
@@ -405,9 +406,8 @@
 {
 	uint32_t cycle;
 
-	if (__predict_true((curthread->flags &
-		(THR_FLAGS_NEED_SUSPEND | THR_FLAGS_SUSPENDED))
-		!= THR_FLAGS_NEED_SUSPEND))
+	if (__predict_true((curthread->flags & (THR_FLAGS_NEED_SUSPEND |
+	    THR_FLAGS_SUSPENDED)) != THR_FLAGS_NEED_SUSPEND))
 		return;
 	if (curthread == _single_thread)
 		return;
@@ -664,7 +664,7 @@
 }
 
 int
-_sigsuspend(const sigset_t * set)
+_sigsuspend(const sigset_t *set)
 {
 	sigset_t newset;
 
@@ -672,7 +672,7 @@
 }
 
 int
-__thr_sigsuspend(const sigset_t * set)
+__thr_sigsuspend(const sigset_t *set)
 {
 	struct pthread *curthread;
 	sigset_t newset;
@@ -698,7 +698,7 @@
 
 int
 _sigtimedwait(const sigset_t *set, siginfo_t *info,
-	const struct timespec * timeout)
+    const struct timespec *timeout)
 {
 	sigset_t newset;
 
@@ -713,7 +713,7 @@
  */
 int
 __thr_sigtimedwait(const sigset_t *set, siginfo_t *info,
-    const struct timespec * timeout)
+    const struct timespec *timeout)
 {
 	struct pthread	*curthread = _get_curthread();
 	sigset_t newset;
diff --git a/share/man/man3/pthread_testcancel.3 b/share/man/man3/pthread_testcancel.3
--- a/share/man/man3/pthread_testcancel.3
+++ b/share/man/man3/pthread_testcancel.3
@@ -34,6 +34,7 @@
 .Dv PTHREAD_CANCEL_ENABLE
 and
 .Dv PTHREAD_CANCEL_DISABLE .
+The function is async-signal-safe.
 .Pp
 The
 .Fn pthread_setcanceltype
@@ -248,6 +249,11 @@
 .St -p1003.1-96 .
 The standard allows implementations to make many more functions
 cancellation points.
+.Pp
+The
+.Fn pthread_setcancelstate
+function is async-signal-safe as required by
+.St -p1003.1-2024 .
 .Sh AUTHORS
 This manual page was written by
 .An David Leonard Aq Mt d@openbsd.org