diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index aa236bd..4534fb9 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -145,6 +145,7 @@
 extern int fsync(int);
 extern int fdatasync(int);
 extern int ftruncate(int, off_t);
+extern int ftruncate64(int, off64_t);
 
 extern int pause(void);
 extern unsigned int alarm(unsigned int);