diff --git a/src/pulsecore/lock-autospawn.c b/src/pulsecore/lock-autospawn.c
index 72806f831..82518dbac 100644
--- a/src/pulsecore/lock-autospawn.c
+++ b/src/pulsecore/lock-autospawn.c
@@ -114,8 +114,15 @@ static void unref(bool after_fork) {
     if (n_ref > 0)
         return;
 
+    /* Join threads only in the process the new thread was created in
+     * to avoid undefined behaviour.
+     * POSIX.1-2008 XSH 2.9.2 Thread IDs: "applications should only assume
+     * that thread IDs are usable and unique within a single process." */
     if (thread) {
-        pa_thread_free(thread);
+        if (after_fork)
+            pa_thread_free_nojoin(thread);
+	else
+            pa_thread_free(thread);
         thread = NULL;
     }
 
diff --git a/src/pulsecore/thread-posix.c b/src/pulsecore/thread-posix.c
index b422ab098..5c19b43f5 100644
--- a/src/pulsecore/thread-posix.c
+++ b/src/pulsecore/thread-posix.c
@@ -127,6 +127,13 @@ void pa_thread_free(pa_thread *t) {
     pa_xfree(t);
 }
 
+void pa_thread_free_nojoin(pa_thread *t) {
+    pa_assert(t);
+
+    pa_xfree(t->name);
+    pa_xfree(t);
+}
+
 int pa_thread_join(pa_thread *t) {
     pa_assert(t);
     pa_assert(t->thread_func);
diff --git a/src/pulsecore/thread.h b/src/pulsecore/thread.h
index 9cabb8995..a6e5f4240 100644
--- a/src/pulsecore/thread.h
+++ b/src/pulsecore/thread.h
@@ -39,6 +39,7 @@ typedef void (*pa_thread_func_t) (void *userdata);
 
 pa_thread* pa_thread_new(const char *name, pa_thread_func_t thread_func, void *userdata);
 void pa_thread_free(pa_thread *t);
+void pa_thread_free_nojoin(pa_thread *t);
 int pa_thread_join(pa_thread *t);
 int pa_thread_is_running(pa_thread *t);
 pa_thread *pa_thread_self(void);