diff --git a/libc/arch-x86_64/syscalls/umask.S b/libc/arch-x86_64/syscalls/umask.S
new file mode 100644
index 0000000..e301c71
--- /dev/null
+++ b/libc/arch-x86_64/syscalls/umask.S
@@ -0,0 +1,17 @@
+/* autogenerated by gensyscalls.py */
+#include <asm/unistd.h>
+#include <linux/err.h>
+#include <machine/asm.h>
+
+ENTRY(umask)
+    movl    $__NR_umask, %eax
+    syscall
+    cmpq    $-MAX_ERRNO, %rax
+    jb      1f
+    negl    %eax
+    movl    %eax, %edi
+    call    __set_errno
+    orq     $-1, %rax
+1:
+    ret
+END(umask)