diff --git a/lib/libc/stdlib/exit.c b/lib/libc/stdlib/exit.c
--- a/lib/libc/stdlib/exit.c
+++ b/lib/libc/stdlib/exit.c
@@ -48,6 +48,8 @@
  */
 int	__isthreaded	= 0;
 
+static pthread_mutex_t exit_mutex = PTHREAD_MUTEX_INITIALIZER;
+
 /*
  * Exit, flushing stdio buffers if necessary.
  */
@@ -59,6 +61,10 @@
 
 	_thread_autoinit_dummy_decl = 1;
 
+	/* Make exit(3) thread-safe */
+	if (__isthreaded)
+		_pthread_mutex_lock(&exit_mutex);
+
 	/*
 	 * We're dealing with cleaning up thread_local destructors in the case of
 	 * the process termination through main() exit.