diff --git a/lib/libthr/tests/atfork_test.c b/lib/libthr/tests/atfork_test.c
--- a/lib/libthr/tests/atfork_test.c
+++ b/lib/libthr/tests/atfork_test.c
@@ -25,6 +25,58 @@
 static int forked;
 static int parent;
 
+/*
+ * We'll disable prefork unless we're specifically running the preinit test to
+ * be sure that we don't mess up any other tests' results.
+ */
+static bool prefork_enabled;
+
+static void
+prefork(void)
+{
+	if (prefork_enabled)
+		forked++;
+}
+
+static void
+registrar(void)
+{
+	pthread_atfork(prefork, NULL, NULL);
+}
+
+static __attribute__((section(".preinit_array"), used))
+void (*preinitfn)(void) = &registrar;
+
+/*
+ * preinit_atfork() just enables the prepare handler that we registered in a
+ * .preinit_array entry and checks that forking actually invoked that callback.
+ * We don't bother testing all three callbacks here because the implementation
+ * doesn't really lend itself to the kind of error where we only have a partial
+ * set of callbacks registered.
+ */
+ATF_TC(preinit_atfork);
+ATF_TC_HEAD(preinit_atfork, tc)
+{
+	atf_tc_set_md_var(tc, "descr",
+	    "Checks that atfork callbacks may be registered in .preinit_array functions");
+}
+ATF_TC_BODY(preinit_atfork, tc)
+{
+	pid_t p;
+
+	(void)signal(SIGCHLD, SIG_IGN);
+	prefork_enabled = true;
+	p = fork();
+
+	ATF_REQUIRE(p >= 0);
+	if (p == 0)
+		_exit(0);
+
+	prefork_enabled = false;
+
+	ATF_REQUIRE(forked != 0);
+}
+
 static void
 basic_prepare(void)
 {
@@ -221,6 +273,7 @@
 
 ATF_TP_ADD_TCS(tp)
 {
+	ATF_TP_ADD_TC(tp, preinit_atfork);
 	ATF_TP_ADD_TC(tp, basic_atfork);
 	ATF_TP_ADD_TC(tp, multi_atfork);
 	return (atf_no_error());
diff --git a/lib/libthr/thread/thr_fork.c b/lib/libthr/thread/thr_fork.c
--- a/lib/libthr/thread/thr_fork.c
+++ b/lib/libthr/thread/thr_fork.c
@@ -84,20 +84,24 @@
 	struct pthread *curthread;
 	struct pthread_atfork *af;
 
-	_thr_check_init();
-
 	if ((af = malloc(sizeof(struct pthread_atfork))) == NULL)
 		return (ENOMEM);
 
-	curthread = _get_curthread();
 	af->prepare = prepare;
 	af->parent = parent;
 	af->child = child;
-	THR_CRITICAL_ENTER(curthread);
-	_thr_rwl_wrlock(&_thr_atfork_lock);
-	TAILQ_INSERT_TAIL(&_thr_atfork_list, af, qe);
-	_thr_rwl_unlock(&_thr_atfork_lock);
-	THR_CRITICAL_LEAVE(curthread);
+
+	if (_thr_initial != NULL) {
+		curthread = _get_curthread();
+		THR_CRITICAL_ENTER(curthread);
+		_thr_rwl_wrlock(&_thr_atfork_lock);
+		TAILQ_INSERT_TAIL(&_thr_atfork_list, af, qe);
+		_thr_rwl_unlock(&_thr_atfork_lock);
+		THR_CRITICAL_LEAVE(curthread);
+	} else {
+		TAILQ_INSERT_TAIL(&_thr_atfork_list, af, qe);
+	}
+
 	return (0);
 }
 
diff --git a/lib/libthr/thread/thr_init.c b/lib/libthr/thread/thr_init.c
--- a/lib/libthr/thread/thr_init.c
+++ b/lib/libthr/thread/thr_init.c
@@ -519,7 +519,6 @@
 		env = getenv("LIBPTHREAD_QUEUE_FIFO");
 		if (env)
 			_thr_queuefifo = atoi(env);
-		TAILQ_INIT(&_thr_atfork_list);
 		env = getenv("LIBPTHREAD_UMTX_MIN_TIMEOUT");
 		if (env) {
 			char *endptr;