diff --git a/src/lib.rs b/src/lib.rs
index 5d84a3c..ed926a7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -99,6 +99,8 @@ pub trait Integer: Sized + Num + PartialOrd + Ord + Eq {
     }
 
     /// Greatest Common Divisor (GCD).
+    /// 
+    /// The result should always be non-negative.
     ///
     /// # Examples
     ///