diff --git a/lib/spack/spack/build_systems/xorg.py b/lib/spack/spack/build_systems/xorg.py
index 131444cbb5e..47ba83d21a3 100644
--- a/lib/spack/spack/build_systems/xorg.py
+++ b/lib/spack/spack/build_systems/xorg.py
@@ -6,12 +6,17 @@
 
 import spack.package_base
 import spack.util.url
+from spack.directives import conflicts
 
 
 class XorgPackage(spack.package_base.PackageBase):
     """Mixin that takes care of setting url and mirrors for x.org
     packages."""
 
+    # x.org packages are not supported on windows or darwin
+    conflicts("platform=windows")
+    conflicts("platform=darwin")
+
     #: Path of the package in a x.org mirror
     xorg_mirror_path: Optional[str] = None
 
diff --git a/var/spack/repos/builtin/packages/glx/package.py b/var/spack/repos/builtin/packages/glx/package.py
index 5ce00b79bf2..22918f0eade 100644
--- a/var/spack/repos/builtin/packages/glx/package.py
+++ b/var/spack/repos/builtin/packages/glx/package.py
@@ -12,6 +12,9 @@ class Glx(BundlePackage):
 
     version("1.4")
 
+    conflicts("platform=windows")
+    conflicts("platform=darwin")
+
     depends_on("libglx")
     provides("gl@4.5")