diff --git a/tools/public_api_guard/core/core.d.ts b/tools/public_api_guard/core/core.d.ts
index d781017237144..1551867f32c14 100644
--- a/tools/public_api_guard/core/core.d.ts
+++ b/tools/public_api_guard/core/core.d.ts
@@ -462,10 +462,10 @@ export interface KeyValueChanges<K, V> {
 }
 
 export interface KeyValueDiffer<K, V> {
-    diff(object: Map<K, V>): KeyValueChanges<K, V>;
+    diff(object: Map<K, V>): KeyValueChanges<K, V> | null;
     diff(object: {
         [key: string]: V;
-    }): KeyValueChanges<string, V>;
+    }): KeyValueChanges<string, V> | null;
 }
 
 export interface KeyValueDifferFactory {