diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index 9cfb918..a2beb38 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -246,6 +246,8 @@
 int getdomainname(char* __buf, size_t __buf_size) __INTRODUCED_IN(26);
 int setdomainname(const char* __name, size_t __n) __INTRODUCED_IN(26);
 
+void swab(const void* __src, void* __dst, ssize_t __byte_count) __INTRODUCED_IN_FUTURE;
+
 #if defined(__BIONIC_INCLUDE_FORTIFY_HEADERS)
 #include <bits/fortify/unistd.h>
 #endif