diff --git a/var/spack/repos/builtin/packages/root/package.py b/var/spack/repos/builtin/packages/root/package.py
index a1a8bb95275..f8d7f82791e 100644
--- a/var/spack/repos/builtin/packages/root/package.py
+++ b/var/spack/repos/builtin/packages/root/package.py
@@ -504,8 +504,8 @@ def cmake_args(self):
 
         # see https://github.com/spack/spack/pull/11579
         if '+python' in self.spec:
-            options.append('-DPYTHON_EXECUTABLE=%s/python' %
-                           self.spec['python'].prefix.bin)
+            options.append('-DPYTHON_EXECUTABLE=%s' %
+                           spec['python'].command.path)
 
         return options