diff --git a/nmigen/compat/fhdl/bitcontainer.py b/nmigen/compat/fhdl/bitcontainer.py
index 648b129..4b91572 100644
--- a/nmigen/compat/fhdl/bitcontainer.py
+++ b/nmigen/compat/fhdl/bitcontainer.py
@@ -18,4 +18,4 @@ def bits_for(n, require_sign_bit=False):
 
 @deprecated("instead of `value_bits_sign(v)`, use `v.shape()`")
 def value_bits_sign(v):
-    return ast.Value.cast(v).shape()
+    return tuple(ast.Value.cast(v).shape())