diff --git a/src/viewport-three/viewport-host.ts b/src/viewport-three/viewport-host.ts
index 21d4651a..392c00b3 100644
--- a/src/viewport-three/viewport-host.ts
+++ b/src/viewport-three/viewport-host.ts
@@ -419,6 +419,12 @@ interface TerrainBrushHit {
   point: Vec3;
 }
 
+interface TerrainGridResizeHit {
+  terrainId: string;
+  side: TerrainGridResizeSide;
+  point: Vec3;
+}
+
 interface LightVolumeRenderObjects {
   group: Group;
   lights: PointLight[];
@@ -442,6 +448,16 @@ interface ActiveTerrainBrushStroke {
   toolState: ArmedTerrainBrushState;
 }
 
+interface ActiveTerrainGridResizeDrag {
+  pointerId: number;
+  side: TerrainGridResizeSide;
+  baseTerrain: Terrain;
+  previewTerrain: Terrain;
+  startPoint: Vec3;
+  outwardDragDistance: number;
+  changed: boolean;
+}
+
 function createTerrainFoliageMaskValueKey(layerId: string, index: number) {
   return `${layerId}\u0000${index}`;
 }