diff --git a/var/spack/repos/builtin/packages/root/package.py b/var/spack/repos/builtin/packages/root/package.py
index 2626f71f801..ff87307f306 100644
--- a/var/spack/repos/builtin/packages/root/package.py
+++ b/var/spack/repos/builtin/packages/root/package.py
@@ -611,7 +611,7 @@ def setup_dependent_build_environment(self, env, dependent_spec):
         env.prepend_path("ROOT_INCLUDE_PATH", dependent_spec.prefix.include)
         if "+rpath" not in self.spec:
             env.prepend_path("LD_LIBRARY_PATH", self.prefix.lib.root)
-        if "platform=darwin" in spec:
+        if "platform=darwin" in self.spec:
             # Newer deployment targets cause fatal errors in rootcling
             env.unset("MACOSX_DEPLOYMENT_TARGET")