diff --git a/lib/spack/spack/platforms/darwin.py b/lib/spack/spack/platforms/darwin.py
index 52284826b1..cfa1d957a1 100644
--- a/lib/spack/spack/platforms/darwin.py
+++ b/lib/spack/spack/platforms/darwin.py
@@ -10,6 +10,7 @@ class Darwin(Platform):
     def __init__(self):
         super(Darwin, self).__init__('darwin')
         self.add_target(self.default, Target(self.default, 'PATH'))
+        self.add_operating_system()
 
     @classmethod
     def detect(self):
diff --git a/lib/spack/spack/platforms/linux.py b/lib/spack/spack/platforms/linux.py
index 7f94d80c34..dcb08569a8 100644
--- a/lib/spack/spack/platforms/linux.py
+++ b/lib/spack/spack/platforms/linux.py
@@ -10,6 +10,7 @@ class Linux(Platform):
     def __init__(self):
         super(Linux, self).__init__('linux')
         self.add_target(self.default, Target(self.default, 'PATH'))
+        self.add_operating_system()
 
     @classmethod
     def detect(self):