diff --git a/src/bigint.rs b/src/bigint.rs
index 336ec7c..1245fcb 100644
--- a/src/bigint.rs
+++ b/src/bigint.rs
@@ -113,16 +113,14 @@ impl BigInt {
         let a_digits = a.inner.len();
         let b_digits = b.inner.len();
 
-        let digits = if b_digits > a_digits {
+        if a_digits == 0 && b_digits == 0 {
+            return 1;
+        }
+
+        if b_digits > a_digits {
             b_digits
         } else {
             a_digits
-        };
-
-        if digits > 0 {
-            digits
-        } else {
-            1
         }
     }
 }
@@ -610,4 +608,24 @@ mod tests {
     fn test_from_large_signed() {
         BigInt::from(128i128);
     }
+
+    #[test]
+    #[should_panic]
+    fn test_from_str() {
+        let str = "012345";
+        BigInt::from(str);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_from_string() {
+        let str = String::from("012345");
+        BigInt::from(str);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_from_str_radix() {
+        BigInt::from_str_radix("123456", 16);
+    }
 }
diff --git a/src/num.rs b/src/num.rs
index 1408486..ff3aeab 100644
--- a/src/num.rs
+++ b/src/num.rs
@@ -151,7 +151,6 @@ macro_rules! impl_int {
                     self == 0
                 }
 
-                #[cfg_attr(tarpaulin, skip)]
                 fn max_value() -> $type {
                     <$type>::max_value()
                 }
@@ -244,7 +243,6 @@ macro_rules! impl_unsigned {
                             let (x, y) = (min(x, y), max(x, y));
                             Self::stein_gcd((y - x) >> 1, x)
                         }
-                        #[cfg_attr(tarpaulin, skip)]
                         _ => unreachable!(),
                     }
                 }