diff --git a/var/spack/packages/openssl/package.py b/var/spack/packages/openssl/package.py
index 4bf1f832d45..43b8771be0f 100644
--- a/var/spack/packages/openssl/package.py
+++ b/var/spack/packages/openssl/package.py
@@ -16,6 +16,8 @@ class Openssl(Package):
     parallel = False
 
     def install(self, spec, prefix):
+        env['KERNEL_BITS'] = '64' # Only on 64-bit Mac
+
         config = Executable("./config")
         config("--prefix=%s" % prefix,
                "--openssldir=%s/etc/openssl" % prefix,