diff --git a/ext/cgi/escape/escape.c b/ext/cgi/escape/escape.c
index 8400e96..5d787d0 100644
--- a/ext/cgi/escape/escape.c
+++ b/ext/cgi/escape/escape.c
@@ -1,14 +1,22 @@
 #include "ruby.h"
 #include "ruby/encoding.h"
+#include "ruby/util.h"
 
 #ifndef HAVE_RB_LEN_T
 typedef long rb_len_t;
+typedef unsigned long rb_ulen_t;
 # define RB_LEN_MAX LONG_MAX
 #endif
 
+#ifndef HAVE_RUBY_SCAN_DIGITS
 RUBY_EXTERN unsigned long ruby_scan_digits(const char *str, ssize_t len, int base, size_t *retlen, int *overflow);
+#endif
+#ifndef HAVE_RUBY_HEXDIGITS_0_
 RUBY_EXTERN const char ruby_hexdigits[];
+#endif
+#ifndef HAVE_RUBY_DIGIT36_TO_NUMBER_TABLE_0_
 RUBY_EXTERN const signed char ruby_digit36_to_number_table[];
+#endif
 #define lower_hexdigits (ruby_hexdigits+0)
 #define upper_hexdigits (ruby_hexdigits+16)
 #define char_to_number(c) ruby_digit36_to_number_table[(unsigned char)(c)]
@@ -99,7 +107,7 @@ optimized_unescape_html(VALUE str)
     cstr = RSTRING_PTR(str);
 
     for (i = 0; i < len; i++) {
-        unsigned long cc;
+        rb_ulen_t cc;
         char c = cstr[i];
         if (c != '&') continue;
         plen = i - beg;
diff --git a/ext/cgi/escape/extconf.rb b/ext/cgi/escape/extconf.rb
index 73acd89..db4c5ca 100644
--- a/ext/cgi/escape/extconf.rb
+++ b/ext/cgi/escape/extconf.rb
@@ -3,5 +3,12 @@
 if RUBY_ENGINE == 'truffleruby'
   File.write("Makefile", dummy_makefile($srcdir).join(""))
 else
+  if have_func(%[ruby_scan_digits()], "ruby/util.h")
+    $defs.pop # defined but no declaration
+  else
+    have_func(%[ruby_scan_digits("", 0, 0, NULL, NULL)], "ruby/util.h")
+  end
+  have_var(%[ruby_hexdigits[0]], "ruby/util.h")
+  have_var(%[ruby_digit36_to_number_table[0]], "ruby/util.h")
   create_makefile 'cgi/escape'
 end