diff --git a/src/rtlil.rs b/src/rtlil.rs
index 29519ca..083deb2 100644
--- a/src/rtlil.rs
+++ b/src/rtlil.rs
@@ -63,7 +63,7 @@ impl SigSpec {
 impl std::fmt::Display for SigSpec {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            SigSpec::Const(val, width) => write!(f, "{}'{}", width, val)?,
+            SigSpec::Const(val, width) => write!(f, "{0}'{2:01$b}", width, *width as usize, val)?,
             SigSpec::Wire(id) => write!(f, "{}", id)?,
         };
         Ok(())