diff --git a/packages/core/src/config/custom-field/custom-field-types.ts b/packages/core/src/config/custom-field/custom-field-types.ts
index 9f3b15b968..dd9a2cbe03 100644
--- a/packages/core/src/config/custom-field/custom-field-types.ts
+++ b/packages/core/src/config/custom-field/custom-field-types.ts
@@ -100,7 +100,7 @@ export type RelationCustomFieldConfig = TypedCustomFieldConfig<
     entity: Type<VendureEntity>;
     graphQLType?: string;
     eager?: boolean;
-    inverseSide: string | ((object: VendureEntity) => any);
+    inverseSide?: string | ((object: VendureEntity) => any);
 };
 
 /**