diff --git a/libc/arch-x86/string/fss.S b/libc/arch-x86/string/fss.S
new file mode 100644
index 0000000..96affab
--- /dev/null
+++ b/libc/arch-x86/string/fss.S
@@ -0,0 +1,17 @@
+/*	$OpenBSD: ffs.S,v 1.3 2005/08/07 11:30:38 espie Exp $ */
+/*
+ * Written by J.T. Conklin <jtc@netbsd.org>.
+ * Public domain.
+ */
+
+#include <machine/asm.h>
+
+ENTRY(ffs)
+	bsfl	4(%esp),%eax
+	jz	L1	 		/* ZF is set if all bits are 0 */
+	incl	%eax			/* bits numbered from 1, not 0 */
+	ret
+
+	.align 2
+L1:	xorl	%eax,%eax		/* clear result */
+	ret