diff --git a/course-source-files/section 12/LinkedStackApp/Stack.h b/course-source-files/section 12/LinkedStackApp/Stack.h
index 362d0f4..0b1a34c 100644
--- a/course-source-files/section 12/LinkedStackApp/Stack.h	
+++ b/course-source-files/section 12/LinkedStackApp/Stack.h	
@@ -6,9 +6,9 @@ class Stack
 	public:
 		virtual void push(int newEntry) = 0;
 		virtual int pop() = 0;
-		virtual int peek() = 0;
-		virtual bool isEmpty() = 0;
+		virtual int peek() const = 0;
+		virtual bool isEmpty() const = 0;
 		virtual void makeEmpty() = 0;
 };
 
-#endif 
\ No newline at end of file
+#endif