diff --git a/jitterbug/utils.py b/jitterbug/utils.py
index 149ffaf..99fc179 100644
--- a/jitterbug/utils.py
+++ b/jitterbug/utils.py
@@ -29,7 +29,7 @@ def make_calculator(method: str, basis: Optional[str], **kwargs) -> Calculator:
     """
 
     if method in mopac_methods:
-        if basis is not None:
+        if not (basis is None or basis == "None"):
             raise ValueError(f'Basis must be none for method: {method}')
         return MOPAC(method=method, command='mopac PREFIX.mop > /dev/null')
     else: