diff --git a/crates/fayalite/src/int.rs b/crates/fayalite/src/int.rs
index 68f1cac..b80c2b6 100644
--- a/crates/fayalite/src/int.rs
+++ b/crates/fayalite/src/int.rs
@@ -488,7 +488,10 @@ impl SInt {
                     v.not().bits().checked_add(1).expect("too big")
                 }
                 Sign::NoSign => 0,
-                Sign::Plus => v.bits(),
+                Sign::Plus => {
+                    // account for sign bit
+                    v.bits().checked_add(1).expect("too big")
+                }
             }
             .try_into()
             .expect("too big"),
@@ -772,3 +775,31 @@ impl ToLiteralBits for bool {
         Ok(interned_bit(*self))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_uint_for_value() {
+        assert_eq!(UInt::for_value(0u8).width, 0);
+        assert_eq!(UInt::for_value(1u8).width, 1);
+        assert_eq!(UInt::for_value(2u8).width, 2);
+        assert_eq!(UInt::for_value(3u8).width, 2);
+        assert_eq!(UInt::for_value(4u8).width, 3);
+    }
+
+    #[test]
+    fn test_sint_for_value() {
+        assert_eq!(SInt::for_value(-5).width, 4);
+        assert_eq!(SInt::for_value(-4).width, 3);
+        assert_eq!(SInt::for_value(-3).width, 3);
+        assert_eq!(SInt::for_value(-2).width, 2);
+        assert_eq!(SInt::for_value(-1).width, 1);
+        assert_eq!(SInt::for_value(0).width, 0);
+        assert_eq!(SInt::for_value(1).width, 2);
+        assert_eq!(SInt::for_value(2).width, 3);
+        assert_eq!(SInt::for_value(3).width, 3);
+        assert_eq!(SInt::for_value(4).width, 4);
+    }
+}