diff --git a/src/field/pokemon.ts b/src/field/pokemon.ts
index 4904964ac1b..f02c9a1f30c 100644
--- a/src/field/pokemon.ts
+++ b/src/field/pokemon.ts
@@ -1781,7 +1781,7 @@ export abstract class Pokemon extends Phaser.GameObjects.Container {
    * @returns Whether this Pokemon is currently fused with another species.
    */
   isFusion(useIllusion = false): boolean {
-    return useIllusion ? !!this.summonData.illusion?.fusionSpecies : !!this.fusionSpecies;
+    return !!(useIllusion ? (this.summonData.illusion?.fusionSpecies ?? this.fusionSpecies) : this.fusionSpecies);
   }
 
   /**