diff --git a/conservancy_beancount/config.py b/conservancy_beancount/config.py
index 82a88370b314274fbcba275815144e2a9d993dc5..55b48d1ab8c13329f436233c3d28e63e70022bf8 100644
--- a/conservancy_beancount/config.py
+++ b/conservancy_beancount/config.py
@@ -81,6 +81,11 @@ class Config:
         try:
             cache_root = Path(os.environ['XDG_CACHE_HOME'])
         except (KeyError, ValueError):
+            ok = False
+        else:
+            # Per the spec, non-absolute paths should be ignored.
+            ok = cache_root.is_absolute()
+        if not ok:
             cache_root = Path.home() / '.cache'
         return (
             self._dir_or_none(cache_root)
diff --git a/tests/test_config.py b/tests/test_config.py
index 2beac9fe8d18cf3c6ba47e8f47227f02c5b6f025..0b45aae0802070e0b3c6f06e8b6b48c4f7261a2b 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -283,6 +283,13 @@ def test_cache_path_parent_conflict(tmp_path):
         config = config_mod.Config()
         assert config.cache_dir_path('TESTcache') is None
 
+def test_relative_xdg_cache_home_ignored(tmp_path):
+    with update_environ(HOME=tmp_path,
+                        XDG_CACHE_HOME='nonexistent/test/cache/directory/tree'):
+        config = config_mod.Config()
+        cache_dir_path = config.cache_dir_path('TESTcache')
+    assert cache_dir_path == tmp_path / '.cache/TESTcache'
+
 def test_payment_threshold():
     threshold = config_mod.Config().payment_threshold()
     assert threshold == 0