diff --git a/src/data/battler-tags.ts b/src/data/battler-tags.ts
index 9ccb06c70ba..70b3f282eb0 100644
--- a/src/data/battler-tags.ts
+++ b/src/data/battler-tags.ts
@@ -2631,7 +2631,10 @@ export class ImprisonTag extends MoveRestrictionBattlerTag {
    * @returns source pokemon {@linkcode Pokemon} or undefined
    */
   private retrieveSource(scene: BattleScene): Pokemon | undefined {
-    return scene.getPokemonById(this.sourceId);
+    if (this.sourceId) {
+      return scene.getPokemonById(this.sourceId) ?? undefined;
+    }
+    return undefined;
   }
 }