diff --git a/var/spack/repos/builtin/packages/intel-tbb/package.py b/var/spack/repos/builtin/packages/intel-tbb/package.py
index 8ef66abafac..aba173496c9 100644
--- a/var/spack/repos/builtin/packages/intel-tbb/package.py
+++ b/var/spack/repos/builtin/packages/intel-tbb/package.py
@@ -135,6 +135,11 @@ def url_for_version(self, version):
             name = '{0}'.format(version)
         return url.format(name)
 
+    # We set OS here in case the user has it set to something else
+    # that TBB doesn't expect.
+    def setup_build_environment(self, env):
+        env.set('OS', platform.system())
+
     def coerce_to_spack(self, tbb_build_subdir):
         for compiler in ["icc", "gcc", "clang"]:
             fs = glob.glob(join_path(tbb_build_subdir,