diff --git a/include/asm-generic/word-at-a-time.h b/include/asm-generic/word-at-a-time.h
index 3f21f1b..d3909ef 100644
--- a/include/asm-generic/word-at-a-time.h
+++ b/include/asm-generic/word-at-a-time.h
@@ -49,4 +49,12 @@
 	return (val + c->high_bits) & ~rhs;
 }
 
+#ifndef zero_bytemask
+#ifdef CONFIG_64BIT
+#define zero_bytemask(mask)	(~0ul << fls64(mask))
+#else
+#define zero_bytemask(mask)	(~0ul << fls(mask))
+#endif /* CONFIG_64BIT */
+#endif /* zero_bytemask */
+
 #endif /* _ASM_WORD_AT_A_TIME_H */