diff --git a/ext/readline/extconf.rb b/ext/readline/extconf.rb
index 737ca749ee..c5db9b029a 100644
--- a/ext/readline/extconf.rb
+++ b/ext/readline/extconf.rb
@@ -1,26 +1,26 @@
 require "mkmf"
 
-$readline_headers = ["stdio.h"]
+readline = Struct.new(:headers, :extra_check).new(["stdio.h"])
 
-def have_readline_header(header)
-  if have_header(header, &$readline_extra_check)
-    $readline_headers.push(header)
+def readline.have_header(header)
+  if super(header, &extra_check)
+    headers.push(header)
     return true
   else
     return false
   end
 end
 
-def have_readline_var(var)
-  return have_var(var, $readline_headers)
+def readline.have_var(var)
+  return super(var, headers)
 end
 
-def have_readline_func(func)
-  return have_func(func, $readline_headers)
+def readline.have_func(func)
+  return super(func, headers)
 end
 
-def have_readline_macro(macro)
-  return have_macro(macro, $readline_headers)
+def readline.have_macro(macro)
+  return super(macro, headers)
 end
 
 dir_config('curses')
@@ -37,66 +37,66 @@ have_library("ncurses", "tgetnum") ||
 case enable_libedit
 when true
   # --enable-libedit
-  unless (have_readline_header("editline/readline.h") ||
-          have_readline_header("readline/readline.h")) &&
+  unless (readline.have_header("editline/readline.h") ||
+          readline.have_header("readline/readline.h")) &&
           have_library("edit", "readline")
     raise "libedit not found"
   end
 when false
   # --disable-libedit
-  unless ((have_readline_header("readline/readline.h") &&
-           have_readline_header("readline/history.h")) &&
+  unless ((readline.have_header("readline/readline.h") &&
+           readline.have_header("readline/history.h")) &&
            have_library("readline", "readline"))
     raise "readline not found"
   end
 else
   # does not specify
-  unless ((have_readline_header("readline/readline.h") &&
-           have_readline_header("readline/history.h")) &&
+  unless ((readline.have_header("readline/readline.h") &&
+           readline.have_header("readline/history.h")) &&
            (have_library("readline", "readline") ||
             have_library("edit", "readline"))) ||
-            (have_readline_header("editline/readline.h") &&
+            (readline.have_header("editline/readline.h") &&
              have_library("edit", "readline"))
     raise "readline nor libedit not found"
   end
 end
 
-have_readline_func("rl_getc")
-have_readline_func("rl_getc_function")
-have_readline_func("rl_filename_completion_function")
-have_readline_func("rl_username_completion_function")
-have_readline_func("rl_completion_matches")
-have_readline_func("rl_refresh_line")
-have_readline_var("rl_deprep_term_function")
-have_readline_var("rl_completion_append_character")
-have_readline_var("rl_basic_word_break_characters")
-have_readline_var("rl_completer_word_break_characters")
-have_readline_var("rl_basic_quote_characters")
-have_readline_var("rl_completer_quote_characters")
-have_readline_var("rl_filename_quote_characters")
-have_readline_var("rl_attempted_completion_over")
-have_readline_var("rl_library_version")
-have_readline_var("rl_editing_mode")
-have_readline_var("rl_line_buffer")
-have_readline_var("rl_point")
+readline.have_func("rl_getc")
+readline.have_func("rl_getc_function")
+readline.have_func("rl_filename_completion_function")
+readline.have_func("rl_username_completion_function")
+readline.have_func("rl_completion_matches")
+readline.have_func("rl_refresh_line")
+readline.have_var("rl_deprep_term_function")
+readline.have_var("rl_completion_append_character")
+readline.have_var("rl_basic_word_break_characters")
+readline.have_var("rl_completer_word_break_characters")
+readline.have_var("rl_basic_quote_characters")
+readline.have_var("rl_completer_quote_characters")
+readline.have_var("rl_filename_quote_characters")
+readline.have_var("rl_attempted_completion_over")
+readline.have_var("rl_library_version")
+readline.have_var("rl_editing_mode")
+readline.have_var("rl_line_buffer")
+readline.have_var("rl_point")
 # workaround for native windows.
-/mswin|bccwin|mingw/ !~ RUBY_PLATFORM && have_readline_var("rl_event_hook")
-/mswin|bccwin|mingw/ !~ RUBY_PLATFORM && have_readline_var("rl_catch_sigwinch")
-/mswin|bccwin|mingw/ !~ RUBY_PLATFORM && have_readline_var("rl_catch_signals")
-have_readline_var("rl_pre_input_hook")
-have_readline_var("rl_special_prefixes")
-have_readline_func("rl_cleanup_after_signal")
-have_readline_func("rl_free_line_state")
-have_readline_func("rl_clear_signals")
-have_readline_func("rl_set_screen_size")
-have_readline_func("rl_get_screen_size")
-have_readline_func("rl_vi_editing_mode")
-have_readline_func("rl_emacs_editing_mode")
-have_readline_func("replace_history_entry")
-have_readline_func("remove_history")
-have_readline_func("clear_history")
-have_readline_func("rl_redisplay")
-have_readline_func("rl_insert_text")
-have_readline_macro("RL_PROMPT_START_IGNORE")
-have_readline_macro("RL_PROMPT_END_IGNORE")
+/mswin|bccwin|mingw/ !~ RUBY_PLATFORM && readline.have_var("rl_event_hook")
+/mswin|bccwin|mingw/ !~ RUBY_PLATFORM && readline.have_var("rl_catch_sigwinch")
+/mswin|bccwin|mingw/ !~ RUBY_PLATFORM && readline.have_var("rl_catch_signals")
+readline.have_var("rl_pre_input_hook")
+readline.have_var("rl_special_prefixes")
+readline.have_func("rl_cleanup_after_signal")
+readline.have_func("rl_free_line_state")
+readline.have_func("rl_clear_signals")
+readline.have_func("rl_set_screen_size")
+readline.have_func("rl_get_screen_size")
+readline.have_func("rl_vi_editing_mode")
+readline.have_func("rl_emacs_editing_mode")
+readline.have_func("replace_history_entry")
+readline.have_func("remove_history")
+readline.have_func("clear_history")
+readline.have_func("rl_redisplay")
+readline.have_func("rl_insert_text")
+readline.have_macro("RL_PROMPT_START_IGNORE")
+readline.have_macro("RL_PROMPT_END_IGNORE")
 create_makefile("readline")