diff --git a/README.md b/README.md
index 564d0395..4c356b4f 100644
--- a/README.md
+++ b/README.md
@@ -139,7 +139,7 @@ To represent this in `IGListKit`'s diffing, add and implement the `IGListDiffabl
 ```swift
 extension User: IGListDiffable {
   func diffIdentifier() -> NSObjectProtocol {
-    return pk
+    return primaryKey
   }
 
   func isEqual(object: Any?) -> Bool {