diff --git a/sm4.cpp b/sm4.cpp
index 786085c4..2c92883e 100644
--- a/sm4.cpp
+++ b/sm4.cpp
@@ -17,6 +17,7 @@ using CryptoPP::byte;
 using CryptoPP::word32;
 using CryptoPP::rotlConstant;
 
+CRYPTOPP_ALIGN_DATA(4)
 const byte S[256] =
 {
     0xD6, 0x90, 0xE9, 0xFE, 0xCC, 0xE1, 0x3D, 0xB7, 0x16, 0xB6, 0x14, 0xC2, 0x28, 0xFB, 0x2C, 0x05,