diff --git a/mrbgems/mruby-string-ext/src/string.c b/mrbgems/mruby-string-ext/src/string.c
index 5a261c422..4e154d2a8 100644
--- a/mrbgems/mruby-string-ext/src/string.c
+++ b/mrbgems/mruby-string-ext/src/string.c
@@ -989,7 +989,11 @@ mrb_str_succ(mrb_state *mrb, mrb_value self)
 }
 
 #ifdef MRB_UTF8_STRING
-extern const char mrb_utf8len_table[];
+static const char utf8len_table[] =
+{
+  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+  0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 3, 3, 4, 0
+};
 
 static mrb_int
 utf8code(unsigned char* p, mrb_int limit)
@@ -999,7 +1003,7 @@ utf8code(unsigned char* p, mrb_int limit)
   if (p[0] < 0x80)
     return p[0];
 
-  len = mrb_utf8len_table[p[0]>>3];
+  len = utf8len_table[p[0]>>3];
   if (len <= limit && len > 1 && (p[1] & 0xc0) == 0x80) {
     if (len == 2)
       return ((p[0] & 0x1f) << 6) + (p[1] & 0x3f);
diff --git a/src/string.c b/src/string.c
index a19cdbcc9..34df8abc7 100644
--- a/src/string.c
+++ b/src/string.c
@@ -239,17 +239,16 @@ mrb_gc_free_str(mrb_state *mrb, struct RString *str)
 
 #ifdef MRB_UTF8_STRING
 
-const char mrb_utf8len_table[] = {
-  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
-  0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 3, 3, 4, 0
-};
-
 #define utf8_islead(c) ((unsigned char)((c)&0xc0) != 0x80)
 
 mrb_int
 mrb_utf8len(const char* p, const char* e)
 {
-  mrb_int len = mrb_utf8len_table[(unsigned char)p[0] >> 3];
+  static const char lengths[] = {
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 3, 3, 4, 0
+  };
+  mrb_int len = lengths[(unsigned char)p[0] >> 3];
   if (len > e - p) return 1;
   switch (len) {
   case 1: