diff --git a/ext/readline/extconf.rb b/ext/readline/extconf.rb
index fcc62921ae37a9..d3e7872e65f5ae 100644
--- a/ext/readline/extconf.rb
+++ b/ext/readline/extconf.rb
@@ -109,5 +109,4 @@ def readline.have_type(type)
   $defs << "-Drl_hook_func_t=Function"
 end
 
-$INCFLAGS << " -I$(top_srcdir)"
 create_makefile("readline")