diff --git a/var/spack/repos/builtin/packages/root/package.py b/var/spack/repos/builtin/packages/root/package.py
index 092e520dc99..e56f0ab9586 100644
--- a/var/spack/repos/builtin/packages/root/package.py
+++ b/var/spack/repos/builtin/packages/root/package.py
@@ -843,6 +843,7 @@ def setup_run_environment(self, env):
         # the following vars are copied from thisroot.sh; silence a cppyy warning
         env.set("CLING_STANDARD_PCH", "none")
         env.set("CPPYY_API_PATH", "none")
+        env.set("CPPYY_BACKEND_LIBRARY", self.prefix.lib.root.libcppyy_backend)
         if "+rpath" not in self.spec:
             env.prepend_path(self.root_library_path, self.prefix.lib.root)