diff --git a/iterator/referencing.hpp b/iterator/referencing.hpp
index bd5cdfdb..beff2428 100644
--- a/iterator/referencing.hpp
+++ b/iterator/referencing.hpp
@@ -37,12 +37,12 @@ namespace cruft::iterator {
         referencing_iterator& operator++()    {                   ++m_base; return *this; }
         referencing_iterator  operator++(int) { auto val = *this; ++m_base; return   val; }
 
-        bool operator== (const referencing_iterator<Base> &rhs) { return m_base == rhs.m_base; }
-        bool operator!= (const referencing_iterator<Base> &rhs) { return m_base != rhs.m_base; }
-        bool operator>= (const referencing_iterator<Base> &rhs) { return m_base >= rhs.m_base; }
-        bool operator<= (const referencing_iterator<Base> &rhs) { return m_base <= rhs.m_base; }
-        bool operator>  (const referencing_iterator<Base> &rhs) { return m_base >  rhs.m_base; }
-        bool operator<  (const referencing_iterator<Base> &rhs) { return m_base <  rhs.m_base; }
+        bool operator== (const referencing_iterator<Base> &rhs) const { return m_base == rhs.m_base; }
+        bool operator!= (const referencing_iterator<Base> &rhs) const { return m_base != rhs.m_base; }
+        bool operator>= (const referencing_iterator<Base> &rhs) const { return m_base >= rhs.m_base; }
+        bool operator<= (const referencing_iterator<Base> &rhs) const { return m_base <= rhs.m_base; }
+        bool operator>  (const referencing_iterator<Base> &rhs) const { return m_base >  rhs.m_base; }
+        bool operator<  (const referencing_iterator<Base> &rhs) const { return m_base <  rhs.m_base; }
 
         const value_type& operator*() const
         { return **m_base; }