diff --git a/libc/arch-arm64/bionic/__set_tls.c b/libc/arch-arm64/bionic/__set_tls.c
index 4eb3ade..0d88d11 100644
--- a/libc/arch-arm64/bionic/__set_tls.c
+++ b/libc/arch-arm64/bionic/__set_tls.c
@@ -26,6 +26,8 @@
  * SUCH DAMAGE.
  */
 
-void __set_tls(void* tls) {
+#include <sys/cdefs.h>
+
+__LIBC_HIDDEN__ void __set_tls(void* tls) {
   asm("msr tpidr_el0, %0" : : "r" (tls));
 }
diff --git a/libc/arch-x86/bionic/__set_tls.c b/libc/arch-x86/bionic/__set_tls.c
index 722ec6f..38ed3c9 100644
--- a/libc/arch-x86/bionic/__set_tls.c
+++ b/libc/arch-x86/bionic/__set_tls.c
@@ -57,7 +57,7 @@
   result->useable = 1;
 }
 
-int __set_tls(void* ptr) {
+__LIBC_HIDDEN__ int __set_tls(void* ptr) {
   struct user_desc tls_descriptor;
   __init_user_desc(&tls_descriptor, true, ptr);
 
diff --git a/libc/arch-x86_64/bionic/__set_tls.c b/libc/arch-x86_64/bionic/__set_tls.c
index cc7a5f4..6845444 100644
--- a/libc/arch-x86_64/bionic/__set_tls.c
+++ b/libc/arch-x86_64/bionic/__set_tls.c
@@ -31,6 +31,6 @@
 
 extern int __arch_prctl(int, unsigned long);
 
-int __set_tls(void* ptr) {
+__LIBC_HIDDEN__ int __set_tls(void* ptr) {
   return __arch_prctl(ARCH_SET_FS, (uintptr_t) ptr);
 }