diff --git a/src/digit.rs b/src/digit.rs
index 47e718e..0657f0a 100644
--- a/src/digit.rs
+++ b/src/digit.rs
@@ -3,7 +3,7 @@ mod types {
 
     pub type SignedDigit = i8;
 
-    pub type DoubleDigit = i16;
+    pub type DoubleDigit = u16;
 }
 
 use crate::ExpType;