diff --git a/reikhelm-core/src/grid.rs b/reikhelm-core/src/grid.rs
index 6eb0352..2dbf681 100644
--- a/reikhelm-core/src/grid.rs
+++ b/reikhelm-core/src/grid.rs
@@ -23,8 +23,11 @@ use crate::geometry::{Point, Rect};
 ///
 /// `Serialize`/`Deserialize` are available whenever `T` itself supports them,
 /// so a `Grid<Tile>` can round-trip through serde while a `Grid<SomeNonSerde>`
-/// simply does not gain those impls.
-#[derive(Clone, Debug, Serialize, Deserialize)]
+/// simply does not gain those impls. Likewise `PartialEq`/`Eq` are derived and
+/// auto-gated on `T`: `Grid<Tile>` is fully `Eq` (so two maps can be compared
+/// directly for determinism tests), while a `Grid<f32>` scratch buffer gains
+/// only `PartialEq`.
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub struct Grid<T> {
     width: u32,
     height: u32,
diff --git a/reikhelm-core/src/map.rs b/reikhelm-core/src/map.rs
index 3bca459..156feac 100644
--- a/reikhelm-core/src/map.rs
+++ b/reikhelm-core/src/map.rs
@@ -38,11 +38,11 @@ pub enum Tile {
 /// data directly; the type intentionally holds nothing visual. The `seed` is
 /// retained for reproducibility — the same seed reproduces this exact map.
 ///
-/// `Map` does not derive `PartialEq`/`Eq` because its `tiles: Grid<Tile>` does
-/// not (the [`crate::grid::Grid`] storage type is generic and only derives the
-/// comparison traits where it chooses to). Equality of two maps is established
-/// via their serde representation instead — see the round-trip test.
-#[derive(Clone, Debug, Serialize, Deserialize)]
+/// `Map` derives `PartialEq`/`Eq`: it has no float fields and `Grid<Tile>` is
+/// `Eq`, so two maps generated from the same seed can be compared directly with
+/// `==` — the cleanest expression of the determinism contract (spec §7). The
+/// serde round-trip test additionally checks byte-stable JSON.
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub struct Map {
     /// The base terrain layer: what tile occupies each cell.
     pub tiles: Grid<Tile>,