diff --git a/src/phases/switch-phase.ts b/src/phases/switch-phase.ts
index 888fb6454fb..f5ce2179715 100644
--- a/src/phases/switch-phase.ts
+++ b/src/phases/switch-phase.ts
@@ -10,10 +10,10 @@ import { SwitchSummonPhase } from "./switch-summon-phase";
  * for the player (if a switch would be valid for the current battle state).
  */
 export class SwitchPhase extends BattlePhase {
-  protected fieldIndex: integer;
-  private switchType: SwitchType;
-  private isModal: boolean;
-  private doReturn: boolean;
+  protected readonly fieldIndex: integer;
+  private readonly switchType: SwitchType;
+  private readonly isModal: boolean;
+  private readonly doReturn: boolean;
 
   /**
      * Creates a new SwitchPhase
diff --git a/src/phases/switch-summon-phase.ts b/src/phases/switch-summon-phase.ts
index 796a6195945..eb1e089543b 100644
--- a/src/phases/switch-summon-phase.ts
+++ b/src/phases/switch-summon-phase.ts
@@ -15,9 +15,9 @@ import { SubstituteTag } from "#app/data/battler-tags";
 import { SwitchType } from "#enums/switch-type";
 
 export class SwitchSummonPhase extends SummonPhase {
-  private switchType: SwitchType;
-  private slotIndex: integer;
-  private doReturn: boolean;
+  private readonly switchType: SwitchType;
+  private readonly slotIndex: integer;
+  private readonly doReturn: boolean;
 
   private lastPokemon: Pokemon;