diff --git a/ext/cbor/extconf.rb b/ext/cbor/extconf.rb
index 38e37fd..3db089d 100644
--- a/ext/cbor/extconf.rb
+++ b/ext/cbor/extconf.rb
@@ -9,7 +9,7 @@
 have_func("rb_str_intern", ["ruby.h"])
 have_func("rb_integer_unpack", ["ruby.h"])
 
-$CFLAGS << %[ -I.. -Wall -O3 -g -std=c99]
+append_cflags(%w[-I.. -Wall -O3 -g -std=c99])
 #$CFLAGS << %[ -DDISABLE_RMEM]
 #$CFLAGS << %[ -DDISABLE_RMEM_REUSE_INTERNAL_FRAGMENT]
 #$CFLAGS << %[ -DDISABLE_BUFFER_READ_REFERENCE_OPTIMIZE]
@@ -17,9 +17,9 @@
 
 if defined?(RUBY_ENGINE) && RUBY_ENGINE == 'rbx'
   # msgpack-ruby doesn't modify data came from RSTRING_PTR(str)
-  $CFLAGS << %[ -DRSTRING_NOT_MODIFIED]
+  append_cflags('-DRSTRING_NOT_MODIFIED')
   # Rubinius C extensions don't grab GVL while rmem is not thread safe
-  $CFLAGS << %[ -DDISABLE_RMEM]
+  append_cflags('-DDISABLE_RMEM')
 end
 
 if warnflags = CONFIG['warnflags']
diff --git a/lib/cbor/version.rb b/lib/cbor/version.rb
index 3156c8e..5f34d6b 100644
--- a/lib/cbor/version.rb
+++ b/lib/cbor/version.rb
@@ -1,3 +1,3 @@
 module CBOR
-	VERSION = "0.5.9.8"
+	VERSION = "0.5.9.9"
 end