diff --git a/lib/spack/spack/binary_distribution.py b/lib/spack/spack/binary_distribution.py
index a406101d2c..233a587244 100644
--- a/lib/spack/spack/binary_distribution.py
+++ b/lib/spack/spack/binary_distribution.py
@@ -24,6 +24,7 @@
 import warnings
 from contextlib import closing, contextmanager
 from gzip import GzipFile
+from typing import Union
 from urllib.error import HTTPError, URLError
 
 import ruamel.yaml as yaml
@@ -502,7 +503,9 @@ def _binary_index():
 
 
 #: Singleton binary_index instance
-binary_index = llnl.util.lang.Singleton(_binary_index)
+binary_index: Union[BinaryCacheIndex, llnl.util.lang.Singleton] = llnl.util.lang.Singleton(
+    _binary_index
+)
 
 
 class NoOverwriteException(spack.error.SpackError):
diff --git a/lib/spack/spack/caches.py b/lib/spack/spack/caches.py
index 69e8c44e26..20c8b9a169 100644
--- a/lib/spack/spack/caches.py
+++ b/lib/spack/spack/caches.py
@@ -5,6 +5,7 @@
 
 """Caches used by Spack to store data"""
 import os
+from typing import Union
 
 import llnl.util.lang
 from llnl.util.filesystem import mkdirp
@@ -34,7 +35,9 @@ def _misc_cache():
 
 
 #: Spack's cache for small data
-misc_cache = llnl.util.lang.Singleton(_misc_cache)
+misc_cache: Union[
+    spack.util.file_cache.FileCache, llnl.util.lang.Singleton
+] = llnl.util.lang.Singleton(_misc_cache)
 
 
 def fetch_cache_location():
@@ -88,4 +91,6 @@ def symlink(self, mirror_ref):
 
 
 #: Spack's local cache for downloaded source archives
-fetch_cache = llnl.util.lang.Singleton(_fetch_cache)
+fetch_cache: Union[
+    spack.fetch_strategy.FsCache, llnl.util.lang.Singleton
+] = llnl.util.lang.Singleton(_fetch_cache)
diff --git a/lib/spack/spack/concretize.py b/lib/spack/spack/concretize.py
index 41a23994e3..3452e42738 100644
--- a/lib/spack/spack/concretize.py
+++ b/lib/spack/spack/concretize.py
@@ -21,6 +21,7 @@
 import tempfile
 from contextlib import contextmanager
 from itertools import chain
+from typing import Union
 
 import archspec.cpu
 
@@ -43,7 +44,9 @@
 from spack.version import Version, VersionList, VersionRange, ver
 
 #: impements rudimentary logic for ABI compatibility
-_abi = llnl.util.lang.Singleton(lambda: spack.abi.ABI())
+_abi: Union[spack.abi.ABI, llnl.util.lang.Singleton] = llnl.util.lang.Singleton(
+    lambda: spack.abi.ABI()
+)
 
 
 @functools.total_ordering
diff --git a/lib/spack/spack/config.py b/lib/spack/spack/config.py
index d31b1dd533..9154593656 100644
--- a/lib/spack/spack/config.py
+++ b/lib/spack/spack/config.py
@@ -36,7 +36,7 @@
 import re
 import sys
 from contextlib import contextmanager
-from typing import Dict, List, Optional
+from typing import Dict, List, Optional, Union
 
 import ruamel.yaml as yaml
 from ruamel.yaml.error import MarkedYAMLError
@@ -838,7 +838,7 @@ def _config():
 
 
 #: This is the singleton configuration instance for Spack.
-config = llnl.util.lang.Singleton(_config)
+config: Union[Configuration, llnl.util.lang.Singleton] = llnl.util.lang.Singleton(_config)
 
 
 def add_from_file(filename, scope=None):
diff --git a/lib/spack/spack/repo.py b/lib/spack/spack/repo.py
index b9c3a39a20..1d62e83fb6 100644
--- a/lib/spack/spack/repo.py
+++ b/lib/spack/spack/repo.py
@@ -1368,7 +1368,7 @@ def create(configuration):
 
 
 #: Singleton repo path instance
-path = llnl.util.lang.Singleton(_path)
+path: Union[RepoPath, llnl.util.lang.Singleton] = llnl.util.lang.Singleton(_path)
 
 # Add the finder to sys.meta_path
 REPOS_FINDER = ReposFinder()
diff --git a/lib/spack/spack/store.py b/lib/spack/spack/store.py
index b588b76968..aa896c43ed 100644
--- a/lib/spack/spack/store.py
+++ b/lib/spack/spack/store.py
@@ -20,6 +20,7 @@
 import contextlib
 import os
 import re
+from typing import Union
 
 import llnl.util.lang
 import llnl.util.tty as tty
@@ -196,7 +197,7 @@ def _store():
 
 
 #: Singleton store instance
-store = llnl.util.lang.Singleton(_store)
+store: Union[Store, llnl.util.lang.Singleton] = llnl.util.lang.Singleton(_store)
 
 
 def _store_root():