diff --git a/types/ember-data/index.d.ts b/types/ember-data/index.d.ts
index dc8edec397..601a45faf3 100644
--- a/types/ember-data/index.d.ts
+++ b/types/ember-data/index.d.ts
@@ -1132,7 +1132,7 @@ export namespace DS {
          * This method unloads all records in the store.
          * It schedules unloading to happen during the next run loop.
          */
-        unloadAll<K extends keyof ModelRegistry>(modelName: K): void;
+        unloadAll<K extends keyof ModelRegistry>(modelName?: K): void;
         /**
          * DEPRECATED:
          * This method has been deprecated and is an alias for store.hasRecordForId, which should
diff --git a/types/ember-data/test/store.ts b/types/ember-data/test/store.ts
index d3641a6c68..9c1194c711 100644
--- a/types/ember-data/test/store.ts
+++ b/types/ember-data/test/store.ts
@@ -205,3 +205,6 @@ declare module 'ember-data/types/registries/serializer' {
 
 assertType<UserAdapter>(store.adapterFor('user'));
 assertType<UserSerializer>(store.serializerFor('user'));
+
+store.unloadAll();
+store.unloadAll('user');
diff --git a/types/ember-data/v2/index.d.ts b/types/ember-data/v2/index.d.ts
index dccf63e890..3afd091ffe 100644
--- a/types/ember-data/v2/index.d.ts
+++ b/types/ember-data/v2/index.d.ts
@@ -1094,7 +1094,7 @@ export namespace DS {
          * This method unloads all records in the store.
          * It schedules unloading to happen during the next run loop.
          */
-        unloadAll<K extends keyof ModelRegistry>(modelName: K): void;
+        unloadAll<K extends keyof ModelRegistry>(modelName?: K): void;
         /**
          * DEPRECATED:
          * This method has been deprecated and is an alias for store.hasRecordForId, which should
diff --git a/types/ember-data/v2/test/store.ts b/types/ember-data/v2/test/store.ts
index f512afd8a7..2584e7bdf3 100644
--- a/types/ember-data/v2/test/store.ts
+++ b/types/ember-data/v2/test/store.ts
@@ -203,3 +203,6 @@ declare module 'ember-data' {
 
 assertType<UserAdapter>(store.adapterFor('user'));
 assertType<UserSerializer>(store.serializerFor('user'));
+
+store.unloadAll();
+store.unloadAll('user');