diff --git a/engines/zvision/action_node.h b/engines/zvision/action_node.h
index cd5c9f3b273..324dba279de 100644
--- a/engines/zvision/action_node.h
+++ b/engines/zvision/action_node.h
@@ -32,7 +32,7 @@ class ZVision;
 class ActionNode {
 public:
 	virtual ~ActionNode() {}
-	virtual bool process(ZVision *engine, uint32 deltaTimeInMillis);
+	virtual bool process(ZVision *engine, uint32 deltaTimeInMillis) = 0;
 };
 
 class NodeTimer : public ActionNode {