diff --git a/var/spack/repos/builtin/packages/r/package.py b/var/spack/repos/builtin/packages/r/package.py
index 837b140bbc..6418d11ebf 100644
--- a/var/spack/repos/builtin/packages/r/package.py
+++ b/var/spack/repos/builtin/packages/r/package.py
@@ -210,6 +210,11 @@ def setup_dependent_build_environment(self, env, dependent_spec):
 
         r_libs_path = ':'.join(r_libs_path)
         env.set('R_LIBS', r_libs_path)
+        # R_LIBS_USER gets set to a directory in HOME/R if it is not set, such as
+        # during package installation with the --vanilla flag. Set it to null
+        # to ensure that it does not point to a directory that may contain R
+        # packages.
+        env.set('R_LIBS_USER', '')
         env.set('R_MAKEVARS_SITE',
                 join_path(self.etcdir, 'Makeconf.spack'))