diff --git a/src/main/cpp/algorithms/datastructures/stack/Stack.h b/src/main/cpp/algorithms/datastructures/stack/Stack.h
index 2758e83..a1ba8f9 100644
--- a/src/main/cpp/algorithms/datastructures/stack/Stack.h
+++ b/src/main/cpp/algorithms/datastructures/stack/Stack.h
@@ -42,7 +42,7 @@ class Stack
   virtual ~Stack() {}
 
   // return the ID the stack implementation
-  virtual int id() { return id_; }
+  virtual int id() const { return id_; }
 
   // return the number of elements in the stack
   virtual int size() = 0;