diff --git a/modules/entity/src/entity_state.ts b/modules/entity/src/entity_state.ts
index aab8653b49..81fb423ffa 100644
--- a/modules/entity/src/entity_state.ts
+++ b/modules/entity/src/entity_state.ts
@@ -9,9 +9,9 @@ export function getInitialEntityState<V>(): EntityState<V> {
 
 export function createInitialStateFactory<V>() {
   function getInitialState(): EntityState<V>;
-  function getInitialState<S extends object>(
-    additionalState: S
-  ): EntityState<V> & S;
+  function getInitialState<S extends EntityState<V>>(
+    additionalState: Omit<S, keyof EntityState<V>>
+  ): S;
   function getInitialState(additionalState: any = {}): any {
     return Object.assign(getInitialEntityState(), additionalState);
   }
diff --git a/modules/entity/src/models.ts b/modules/entity/src/models.ts
index 4138e3e960..be18b7951e 100644
--- a/modules/entity/src/models.ts
+++ b/modules/entity/src/models.ts
@@ -110,7 +110,9 @@ export interface EntityAdapter<T> extends EntityStateAdapter<T> {
   selectId: IdSelector<T>;
   sortComparer: false | Comparer<T>;
   getInitialState(): EntityState<T>;
-  getInitialState<S extends object>(state: S): EntityState<T> & S;
+  getInitialState<S extends EntityState<T>>(
+    state: Omit<S, keyof EntityState<T>>
+  ): S;
   getSelectors(): EntitySelectors<T, EntityState<T>>;
   getSelectors<V>(
     selectState: (state: V) => EntityState<T>