diff --git a/src/bigint.rs b/src/bigint.rs
index c47bf88..1e6cf67 100644
--- a/src/bigint.rs
+++ b/src/bigint.rs
@@ -175,15 +175,9 @@ impl Sub for BigInt {
             let a = *self.inner.get(i).unwrap_or(&0usize);
             let b = *rhs.inner.get(i).unwrap_or(&0usize);
 
-            if a > 0 && (a - borrow) >= b {
+            if a >= borrow && (a - borrow) >= b {
                 let res = a - b - borrow;
 
-                // Don't add an extra zero if you borrowed everything
-                // from the most significant digit
-                if res == 0 && digits > 0 && i == digits -1 {
-                    return out;
-                }
-
                 out.inner.push(res);
                 borrow = 0;
             } else  {
@@ -462,9 +456,9 @@ mod tests {
         let a = BigInt::new();
         let b = BigInt::new();
 
-        // let c = a.clone() - b.clone();
-        // assert_eq!(a.clone(), b.clone());
-        // assert_eq!(c, a.clone());
+        let c = a.clone() - b.clone();
+        assert_eq!(a.clone(), b.clone());
+        assert_eq!(c, a.clone());
 
         let c = a.clone() + b.clone();
         assert_eq!(a.clone(), b.clone());