diff --git a/src/string.c b/src/string.c
index 5c3ef90cd..d0805758a 100644
--- a/src/string.c
+++ b/src/string.c
@@ -572,6 +572,7 @@ str_index_str_by_char(mrb_state *mrb, mrb_value str, mrb_value sub, mrb_int pos)
    * takes unsigned char*
    * returns mrb_int
    * alignment adjustment added
+   * support bigendian CPU
 */
 static inline mrb_int
 mrb_memsearch_ss(const unsigned char *xs, long m, const unsigned char *ys, long n)
@@ -587,6 +588,15 @@ mrb_memsearch_ss(const unsigned char *xs, long m, const unsigned char *ys, long
 #define MASK2 0x7f7f7f7flu
 #define MASK3 0x80808080lu
 #endif
+#if defined(MRB_ENDIAN_BIG)
+#ifdef MRB_64BIT
+#define MASK4 0x8000000000000000llu
+#else
+#define MASK4 0x80000000
+#endif
+#else
+#define MASK4 0x80
+#endif
 
 #if ALIGNED_WORD_ACCESS
   if ((uintptr_t)ys % sizeof(bitint)) {
@@ -611,14 +621,18 @@ mrb_memsearch_ss(const unsigned char *xs, long m, const unsigned char *ys, long
     size_t j = 0;
 
     while (zeros) {
-      if (zeros & 0x80) {
+      if (zeros & MASK4) {
         const char* substr = (char*)s0 + j + 1;
         if (memcmp(substr, xs + 1, m - 2) == 0) {
           return i + j;
         }
       }
 
+#if defined(MRB_ENDIAN_BIG)
+      zeros <<= 8;
+#else
       zeros >>= 8;
+#endif
       j += 1;
     }
   }