diff --git a/var/spack/repos/builtin/packages/boost/package.py b/var/spack/repos/builtin/packages/boost/package.py
index db72c062121..cc774b927be 100644
--- a/var/spack/repos/builtin/packages/boost/package.py
+++ b/var/spack/repos/builtin/packages/boost/package.py
@@ -329,7 +329,9 @@ def determine_b2_options(self, spec, options):
 
         # Deal with C++ standard.
         if spec.satisfies('@1.66:'):
-            options.append('cxxstd={0}'.format(spec.variants['cxxstd'].value))
+            if spec.variants['cxxstd'].value != 'default':
+                options.append('cxxstd={0}'.format(
+                    spec.variants['cxxstd'].value))
         else:  # Add to cxxflags for older Boost.
             flag = self.cxxstd_to_flag(spec.variants['cxxstd'].value)
             if flag: