diff --git a/src/marble_engine.rs b/src/marble_engine.rs
index e82848d..29af792 100644
--- a/src/marble_engine.rs
+++ b/src/marble_engine.rs
@@ -116,7 +116,7 @@ impl Machine {
 					Tile::Digit(d) => {
 						let new_val = value
 							.wrapping_mul(10)
-							.wrapping_add((*d - b'0') as MarbleValue);
+							.wrapping_add(*d as MarbleValue);
 						*target = Tile::Marble {
 							value: new_val,
 							dir,