diff --git a/js/src/moz.build b/js/src/moz.build
index c0cef9929..3e6402f71 100644
--- a/js/src/moz.build
+++ b/js/src/moz.build
@@ -687,8 +687,8 @@ if CONFIG['_MSC_VER']:
     elif CONFIG['CPU_ARCH'] == 'x86_64' and CONFIG['JS_HAS_CTYPES']:
         SOURCES['ctypes/CTypes.cpp'].no_pgo = True # Bug 810661
     # Prevent floating point errors caused by VC++ optimizations
-    # XXX We should add this to CXXFLAGS, too?
     CFLAGS += ['-fp:precise']
+    CXXFLAGS += ['-fp:precise']    
     # C4805 warns mixing bool with other integral types in computation.
     # But given the conversion from bool is specified, and this is a
     # pattern widely used in code in js/src, suppress this warning here.