diff --git a/ext/redcloth_scan/extconf.rb b/ext/redcloth_scan/extconf.rb
index 506d4a3..edd46c4 100644
--- a/ext/redcloth_scan/extconf.rb
+++ b/ext/redcloth_scan/extconf.rb
@@ -1,6 +1,6 @@
 require 'mkmf'
 CONFIG['warnflags'].gsub!(/-Wshorten-64-to-32/, '') if CONFIG['warnflags']
-$CFLAGS << ' -O0 -Wall ' if CONFIG['CC'] =~ /gcc/
+$CFLAGS << ' -O0 -Wall -fsigned-char' if CONFIG['CC'] =~ /gcc/
 dir_config("redcloth_scan")
 have_library("c", "main")
 create_makefile("redcloth_scan")