diff --git a/include/qpdf/QPDFNameTreeObjectHelper.hh b/include/qpdf/QPDFNameTreeObjectHelper.hh
index 1815676..866d0ef 100644
--- a/include/qpdf/QPDFNameTreeObjectHelper.hh
+++ b/include/qpdf/QPDFNameTreeObjectHelper.hh
@@ -79,6 +79,7 @@ class QPDFNameTreeObjectHelper: public QPDFObjectHelper
     {
         friend class QPDFNameTreeObjectHelper;
       public:
+        virtual ~iterator() = default;
         QPDF_DLL
         bool valid() const;
         QPDF_DLL
diff --git a/include/qpdf/QPDFNumberTreeObjectHelper.hh b/include/qpdf/QPDFNumberTreeObjectHelper.hh
index 7343978..86b076c 100644
--- a/include/qpdf/QPDFNumberTreeObjectHelper.hh
+++ b/include/qpdf/QPDFNumberTreeObjectHelper.hh
@@ -98,6 +98,7 @@ class QPDFNumberTreeObjectHelper: public QPDFObjectHelper
     {
         friend class QPDFNumberTreeObjectHelper;
       public:
+        virtual ~iterator() = default;
         QPDF_DLL
         bool valid() const;
         QPDF_DLL
diff --git a/libqpdf/qpdf/NNTree.hh b/libqpdf/qpdf/NNTree.hh
index 4a843a7..6ad1b32 100644
--- a/libqpdf/qpdf/NNTree.hh
+++ b/libqpdf/qpdf/NNTree.hh
@@ -23,6 +23,7 @@ class NNTreeIterator: public std::iterator<
 {
     friend class NNTreeImpl;
   public:
+    virtual ~NNTreeIterator() = default;
     bool valid() const;
     NNTreeIterator& operator++();
     NNTreeIterator operator++(int)