diff --git a/07/runtime.h b/07/runtime.h
index 2a585b1..baaaaae 100644
--- a/07/runtime.h
+++ b/07/runtime.h
@@ -55,6 +55,7 @@ struct stack {
     struct node_base** data;
 };
 
+void stack_init(struct stack* s);
 void stack_free(struct stack* s);
 void stack_push(struct stack* s, struct node_base* n);
 struct node_base* stack_pop(struct stack* s);
diff --git a/08/runtime.h b/08/runtime.h
index 2a585b1..baaaaae 100644
--- a/08/runtime.h
+++ b/08/runtime.h
@@ -55,6 +55,7 @@ struct stack {
     struct node_base** data;
 };
 
+void stack_init(struct stack* s);
 void stack_free(struct stack* s);
 void stack_push(struct stack* s, struct node_base* n);
 struct node_base* stack_pop(struct stack* s);