diff --git a/crates/border-wars/src/hex.rs b/crates/border-wars/src/hex.rs
index b02c530..03ae69e 100644
--- a/crates/border-wars/src/hex.rs
+++ b/crates/border-wars/src/hex.rs
@@ -2,9 +2,9 @@
 
 use std::collections::HashSet;
 use std::hash::Hash;
-use std::ops;
+use std::ops::{Add, AddAssign, Sub, SubAssign};
 
-use num::Signed;
+use num::{FromPrimitive, Signed};
 use partial_min_max::{max, min};
 
 /// Represents a number that can be used in a hexagonal grid.
@@ -88,7 +88,7 @@ impl<T: HexNumber + Eq + Hash + std::cmp::PartialOrd + num::ToPrimitive> HexPosi
     }
 }
 
-impl<T: HexNumber> ops::Add<Self> for HexPosition<T> {
+impl<T: HexNumber> Add<Self> for HexPosition<T> {
     type Output = Self;
 
     fn add(self, other: Self) -> Self::Output {
@@ -99,13 +99,14 @@ impl<T: HexNumber> ops::Add<Self> for HexPosition<T> {
     }
 }
 
-impl<T: HexNumber> ops::AddAssign<Self> for HexPosition<T> {
+impl<T: HexNumber + AddAssign> AddAssign<Self> for HexPosition<T> {
     fn add_assign(&mut self, other: Self) {
-        *self = *self + other;
+        self.q += other.q;
+        self.r += other.r;
     }
 }
 
-impl<T: HexNumber> ops::Sub<Self> for HexPosition<T> {
+impl<T: HexNumber> Sub<Self> for HexPosition<T> {
     type Output = Self;
 
     fn sub(self, other: Self) -> Self {
@@ -116,8 +117,9 @@ impl<T: HexNumber> ops::Sub<Self> for HexPosition<T> {
     }
 }
 
-impl<T: HexNumber> ops::SubAssign<Self> for HexPosition<T> {
+impl<T: HexNumber + SubAssign> SubAssign<Self> for HexPosition<T> {
     fn sub_assign(&mut self, other: Self) {
-        *self = *self - other;
+        self.q -= other.q;
+        self.r -= other.r;
     }
 }