diff --git a/amaranth/hdl/_ast.py b/amaranth/hdl/_ast.py
index 3f87e9e44..37dd21c66 100644
--- a/amaranth/hdl/_ast.py
+++ b/amaranth/hdl/_ast.py
@@ -73,7 +73,7 @@ def __init__(self, width=1, signed=False):
                             f"not {width}")
         if signed and width <= 0:
             raise TypeError(f"Width of a signed value must be a positive integer, not {width}")
-        self._width = width
+        self._width = operator.index(width)
         self._signed = bool(signed)
 
     @property