diff --git a/src/db/ModelRelation.ts b/src/db/ModelRelation.ts
index 6a1c54b..71f68fc 100644
--- a/src/db/ModelRelation.ts
+++ b/src/db/ModelRelation.ts
@@ -72,7 +72,7 @@ export default abstract class ModelRelation<S extends Model, O extends Model, R
     public async eagerLoad(relations: ModelRelation<S, O, R>[], subRelations: string[] = []): Promise<ModelQueryResult<O>> {
         const ids = relations.map(r => r.getModelID())
             .filter(id => id !== null && id !== undefined)
-            .reduce((array: O[], val) => val in array ? array : [...array, val], []);
+            .reduce((array: O[], val) => array.indexOf(val) >= 0 ? array : [...array, val], []);
         if (ids.length === 0) return [];
 
         const query = this.makeQuery();
@@ -181,7 +181,7 @@ export class ManyThroughModelRelation<S extends Model, O extends Model> extends
 
     public async eagerLoad(relations: ModelRelation<S, O, O[]>[], subRelations: string[] = []): Promise<ModelQueryResult<O>> {
         const ids = relations.map(r => r.getModelID())
-            .reduce((array: O[], val) => val in array ? array : [...array, val], []);
+            .reduce((array: O[], val) => array.indexOf(val) >= 0 ? array : [...array, val], []);
         if (ids.length === 0) return [];
 
         const query = this.makeQuery();