diff --git a/agb/src/number.rs b/agb/src/number.rs
index 004f5154..b5fb06a7 100644
--- a/agb/src/number.rs
+++ b/agb/src/number.rs
@@ -27,7 +27,7 @@ where
     T: Into<Num<N>>,
 {
     fn add_assign(&mut self, rhs: T) {
-        self.0 += (*self + rhs.into()).0
+        self.0 = (*self + rhs.into()).0
     }
 }