diff --git a/src/fr_sp1.rs b/src/fr_sp1.rs
index 1683149..f38a2e0 100644
--- a/src/fr_sp1.rs
+++ b/src/fr_sp1.rs
@@ -458,7 +458,7 @@ impl Neg for Fr {
 
     #[inline]
     fn neg(self) -> Fr {
-        -&self
+        unimplemented!()
     }
 }