diff --git a/src/field/pokemon.ts b/src/field/pokemon.ts
index 3cd25e4d10a..890c6bab0d6 100644
--- a/src/field/pokemon.ts
+++ b/src/field/pokemon.ts
@@ -6916,10 +6916,10 @@ export class EnemyPokemon extends Pokemon {
 
     if (
       speciesId in Overrides.OPP_FORM_OVERRIDES &&
-      Overrides.OPP_FORM_OVERRIDES[speciesId] &&
+      !isNullOrUndefined(Overrides.OPP_FORM_OVERRIDES[speciesId]) &&
       this.species.forms[Overrides.OPP_FORM_OVERRIDES[speciesId]]
     ) {
-      this.formIndex = Overrides.OPP_FORM_OVERRIDES[speciesId] ?? 0;
+      this.formIndex = Overrides.OPP_FORM_OVERRIDES[speciesId];
     }
 
     if (!dataSource) {
diff --git a/src/phases/select-starter-phase.ts b/src/phases/select-starter-phase.ts
index 103174a4c83..0f4360b0af6 100644
--- a/src/phases/select-starter-phase.ts
+++ b/src/phases/select-starter-phase.ts
@@ -53,6 +53,7 @@ export class SelectStarterPhase extends Phase {
       let starterFormIndex = Math.min(starterProps.formIndex, Math.max(starter.species.forms.length - 1, 0));
       if (
         starter.species.speciesId in Overrides.STARTER_FORM_OVERRIDES &&
+        !Utils.isNullOrUndefined(Overrides.STARTER_FORM_OVERRIDES[starter.species.speciesId]) &&
         starter.species.forms[Overrides.STARTER_FORM_OVERRIDES[starter.species.speciesId]!]
       ) {
         starterFormIndex = Overrides.STARTER_FORM_OVERRIDES[starter.species.speciesId]!;