1 files changed, 1 insertions, 2 deletions
diff --git a/mdpoly/types.py b/mdpoly/types.py
index 4b75e8f..a8ffd90 100644
--- a/mdpoly/types.py
+++ b/mdpoly/types.py
@@ -146,8 +146,7 @@ class PolyIndex(tuple[PolyVarIndex]):
     def is_constant(index: Self) -> bool:
         """ Check if is index of a constant term """
         if len(index) != 1:
-            # FIXME: error message
-            raise IndexError(f"{index}")
+            return False
 
         return PolyVarIndex.is_constant(index[0])