diff --git a/src/blackmisc/iterator.h b/src/blackmisc/iterator.h
index af845b01e..27991a46e 100644
--- a/src/blackmisc/iterator.h
+++ b/src/blackmisc/iterator.h
@@ -191,6 +191,12 @@ namespace BlackMisc
             bool operator >=(const ConditionalIterator &other) const { return m_iterator >= other.m_iterator; }
             //! @}
 
+            //! \private
+            void checkEnd(const ConditionalIterator &other) // debugging
+            {
+                Q_ASSERT(m_end == other.m_end && m_end == other.m_iterator);
+            }
+
         private:
             I m_iterator;
             I m_end;
diff --git a/src/blackmisc/range.h b/src/blackmisc/range.h
index dc075347e..fc797f8f3 100644
--- a/src/blackmisc/range.h
+++ b/src/blackmisc/range.h
@@ -124,7 +124,7 @@ namespace BlackMisc
         //! @}
 
         //! Constructor.
-        CRange(I begin, I end) : m_begin(begin), m_end(end) {}
+        CRange(I begin, I end) : m_begin(begin), m_end(end) { check(begin, end); }
 
         //! Begin and end iterators.
         //! @{
@@ -168,6 +168,12 @@ namespace BlackMisc
     private:
         I m_begin;
         I m_end;
+
+        void check(...) {};
+        template <class I2, class F> void check(Iterators::ConditionalIterator<I2, F> begin, Iterators::ConditionalIterator<I2, F> end)
+        {
+            begin.checkEnd(end);
+        }
     };
 
     /*!