diff --git a/arch/alpha/include/asm/word-at-a-time.h b/arch/alpha/include/asm/word-at-a-time.h
index 6b340d0f1521c3ad9c4edf984abe60982ae24c04..902e6ab00a066fead53614ed86cb88980aea2fba 100644
--- a/arch/alpha/include/asm/word-at-a-time.h
+++ b/arch/alpha/include/asm/word-at-a-time.h
@@ -52,4 +52,6 @@ static inline unsigned long find_zero(unsigned long bits)
 #endif
 }
 
+#define zero_bytemask(mask) ((2ul << (find_zero(mask) * 8)) - 1)
+
 #endif /* _ASM_WORD_AT_A_TIME_H */
diff --git a/arch/tile/include/asm/word-at-a-time.h b/arch/tile/include/asm/word-at-a-time.h
index 9e5ce0d7b292160d5f544fcda08c00ea6c04f168..b66a693c2c3453e4f4642fea133890ab268a32d8 100644
--- a/arch/tile/include/asm/word-at-a-time.h
+++ b/arch/tile/include/asm/word-at-a-time.h
@@ -6,7 +6,7 @@
 struct word_at_a_time { /* unused */ };
 #define WORD_AT_A_TIME_CONSTANTS {}
 
-/* Generate 0x01 byte values for non-zero bytes using a SIMD instruction. */
+/* Generate 0x01 byte values for zero bytes using a SIMD instruction. */
 static inline unsigned long has_zero(unsigned long val, unsigned long *data,
 				     const struct word_at_a_time *c)
 {
@@ -33,4 +33,10 @@ static inline long find_zero(unsigned long mask)
 #endif
 }
 
+#ifdef __BIG_ENDIAN
+#define zero_bytemask(mask) (~1ul << (63 - __builtin_clzl(mask)))
+#else
+#define zero_bytemask(mask) ((2ul << __builtin_ctzl(mask)) - 1)
+#endif
+
 #endif /* _ASM_WORD_AT_A_TIME_H */