diff --git a/amaranth/lib/io.py b/amaranth/lib/io.py
index b0fb305..c703213 100644
--- a/amaranth/lib/io.py
+++ b/amaranth/lib/io.py
@@ -12,8 +12,8 @@ def pin_layout(width, dir, xdr=0):
 
     See :class:`Pin` for details.
     """
-    if not isinstance(width, int) or width < 1:
-        raise TypeError("Width must be a positive integer, not {!r}"
+    if not isinstance(width, int) or width < 0:
+        raise TypeError("Width must be a non-negative integer, not {!r}"
                         .format(width))
     if dir not in ("i", "o", "oe", "io"):
         raise TypeError("Direction must be one of \"i\", \"o\", \"io\", or \"oe\", not {!r}"""