diff --git a/nomenclature/codelist.py b/nomenclature/codelist.py
index 685bb483..d94c780c 100644
--- a/nomenclature/codelist.py
+++ b/nomenclature/codelist.py
@@ -622,7 +622,7 @@ def validate_units(
             (variable, unit, self.mapping[variable].unit)
             for variable, unit in unit_mapping.items()
             if variable in self.variables
-            and not set(unit) == set(self.mapping[variable].unit)
+            and unit not in self.mapping[variable].unit
         ]:
             lst = [
                 f"'{v}' - expected: {'one of ' if isinstance(e, list) else ''}"