diff --git a/repos/libports/src/lib/libc/pthread.cc b/repos/libports/src/lib/libc/pthread.cc
index 8481dac372..b0cf0a67e2 100644
--- a/repos/libports/src/lib/libc/pthread.cc
+++ b/repos/libports/src/lib/libc/pthread.cc
@@ -25,6 +25,7 @@
 #include <errno.h>
 #include <pthread.h>
 #include <semaphore.h>
+#include <stdio.h>  /* __isthreaded */
 #include <stdlib.h> /* malloc, free */
 
 /* libc-internal includes */
@@ -74,6 +75,9 @@ size_t Pthread::_tls_pointer_offset;
 
 void Libc::Pthread::Thread_object::entry()
 {
+	/* use threaded mode in FreeBSD libc code */
+	__isthreaded = 1;
+
 	/*
 	 * Obtain stack attributes of new thread for
 	 * 'pthread_attr_get_np()'
diff --git a/repos/libports/src/lib/libc/pthread_create.cc b/repos/libports/src/lib/libc/pthread_create.cc
index aa442a113a..ec5d1a3b51 100644
--- a/repos/libports/src/lib/libc/pthread_create.cc
+++ b/repos/libports/src/lib/libc/pthread_create.cc
@@ -22,6 +22,7 @@
 /* libc includes */
 #include <libc/allocator.h>
 #include <errno.h>
+#include <stdio.h> /* __isthreaded */
 
 /* libc-internal includes */
 #include <internal/init.h>
@@ -172,6 +173,10 @@ int Libc::pthread_create_from_thread(pthread_t *thread, Thread &t, void *stack_a
 		return EAGAIN;
 
 	*thread = thread_obj;
+
+	/* use threaded mode in FreeBSD libc code */
+	__isthreaded = 1;
+
 	return 0;
 }