diff --git a/include/yaml-cpp/contrib/graphbuilder.h b/include/yaml-cpp/contrib/graphbuilder.h
index 7c2159b..f0a38f2 100644
--- a/include/yaml-cpp/contrib/graphbuilder.h
+++ b/include/yaml-cpp/contrib/graphbuilder.h
@@ -19,6 +19,8 @@ class Parser;
 //   functions.
 class GraphBuilderInterface {
  public:
+  virtual ~GraphBuilderInterface() = 0;
+
   // Create and return a new node with a null value.
   virtual void *NewNull(const Mark &mark, void *pParentNode) = 0;