diff --git a/cf_pandas/accessor.py b/cf_pandas/accessor.py
index 899d10c..6b9679f 100644
--- a/cf_pandas/accessor.py
+++ b/cf_pandas/accessor.py
@@ -161,7 +161,11 @@ def keys(self) -> Set[str]:
 
         varnames = list(self.axes) + list(self.coordinates)
         try:
-            varnames.extend(list(self.custom_keys))
+            # see which custom keys have matched values in object
+            matched_keys = [
+                key for key, val in self.custom_keys.items() if len(val) > 0
+            ]
+            varnames.extend(matched_keys)
         except ValueError:
             # don't have criteria defined, then no custom keys to report
             pass
diff --git a/tests/test_accessor.py b/tests/test_accessor.py
index dba8455..e594dac 100644
--- a/tests/test_accessor.py
+++ b/tests/test_accessor.py
@@ -16,6 +16,7 @@
     "temp2": {
         "standard_name": "temp$",
     },
+    "salt2": {"standard_name": "sal$"},
 }
 
 
@@ -73,6 +74,7 @@ def test_match_criteria_key_accessor():
         ]
         assert "X" in df.cf
         assert "Y" not in df.cf
+        assert "salt2" not in df.cf
 
 
 @mock.patch("requests.get")