diff --git a/src/json.hpp b/src/json.hpp
index 2c4fcc6f..6e5f515a 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -5501,7 +5501,7 @@ class basic_json
             }
 
             /// inequality operator (needed for range-based for)
-            bool operator!= (const iteration_proxy_internal& o)
+            bool operator!= (const iteration_proxy_internal& o) const
             {
                 return anchor != o.anchor;
             }
diff --git a/src/json.hpp.re2c b/src/json.hpp.re2c
index a5cf1db4..09bba9cd 100644
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -5501,7 +5501,7 @@ class basic_json
             }
 
             /// inequality operator (needed for range-based for)
-            bool operator!= (const iteration_proxy_internal& o)
+            bool operator!= (const iteration_proxy_internal& o) const
             {
                 return anchor != o.anchor;
             }