diff --git a/var/spack/repos/builtin/packages/libunwind/package.py b/var/spack/repos/builtin/packages/libunwind/package.py
index 6a78fe1ca88..ed0c824d1e2 100644
--- a/var/spack/repos/builtin/packages/libunwind/package.py
+++ b/var/spack/repos/builtin/packages/libunwind/package.py
@@ -31,5 +31,8 @@ class Libunwind(AutotoolsPackage):
     homepage = "http://www.nongnu.org/libunwind/"
     url      = "http://download.savannah.gnu.org/releases/libunwind/libunwind-1.1.tar.gz"
 
+    conflicts('platform=darwin',
+              msg='Non-GNU libunwind needs ELF libraries Darwin does not have')
+
     version('1.2.1', '06ba9e60d92fd6f55cd9dadb084df19e')
     version('1.1', 'fb4ea2f6fbbe45bf032cd36e586883ce')