diff -urp passenger-release-4.0.18.orig/build/basics.rb passenger-release-4.0.18/build/basics.rb
--- passenger-release-4.0.18.orig/build/basics.rb	2013-09-17 13:47:54.000000000 -0500
+++ passenger-release-4.0.18/build/basics.rb	2013-09-23 16:11:12.926455965 -0500
@@ -138,7 +138,7 @@ LIBEXT   = PlatformInfo.library_extensio
 USE_DMALLOC = boolean_option('USE_DMALLOC')
 USE_EFENCE  = boolean_option('USE_EFENCE')
 USE_ASAN    = boolean_option('USE_ASAN')
-OPTIMIZATION_FLAGS = "#{PlatformInfo.debugging_cflags} -DPASSENGER_DEBUG -DBOOST_DISABLE_ASSERTS -fcommon".strip
+OPTIMIZATION_FLAGS = "#{ENV['CXXFLAGS']} #{PlatformInfo.debugging_cflags} -DPASSENGER_DEBUG -DBOOST_DISABLE_ASSERTS -fcommon".strip
 OPTIMIZATION_FLAGS << " -O" if OPTIMIZE
 OPTIMIZATION_FLAGS << " -feliminate-unused-debug-symbols -feliminate-unused-debug-types" if PlatformInfo.compiler_supports_feliminate_unused_debug?
 OPTIMIZATION_FLAGS << " -fvisibility=hidden -DVISIBILITY_ATTRIBUTE_SUPPORTED" if PlatformInfo.compiler_supports_visibility_flag?