diff --git a/ext/c/extconf.rb b/ext/c/extconf.rb
index 8cb21ae..0041a56 100644
--- a/ext/c/extconf.rb
+++ b/ext/c/extconf.rb
@@ -1,13 +1,11 @@
 require 'mkmf'
 
-have_header('ruby.h')
-
-$CFLAGS << ' -Wextra -Wall -pedantic'
+if RbConfig::CONFIG['cc'] =~ /clang|gcc/
+  $CFLAGS << ' -pedantic'
+end
 
 if ENV['DEBUG']
   $CFLAGS << ' -O0 -g'
-else
-  $CFLAGS << ' -O3'
 end
 
 create_makefile('liboga')