diff --git a/include/nlohmann/detail/meta/type_traits.hpp b/include/nlohmann/detail/meta/type_traits.hpp
index 5106a14ba..e9bf81d08 100644
--- a/include/nlohmann/detail/meta/type_traits.hpp
+++ b/include/nlohmann/detail/meta/type_traits.hpp
@@ -450,18 +450,13 @@ decltype(ComparatorType()(std::declval<ObjectKeyType const&>(), std::declval<Key
     static constexpr bool value = true;
 };
 
-template<typename BasicJsonType>
-class iter_impl;
-
 template<typename BasicJsonType, typename KeyType>
 struct is_usable_as_key_type
 {
     static constexpr bool value =
         is_key_type_comparable<typename BasicJsonType::object_comparator_t, typename BasicJsonType::object_t::key_type, KeyType>::value &&
         !std::is_same<KeyType, typename BasicJsonType::iterator>::value &&
-        !std::is_same<KeyType, typename BasicJsonType::const_iterator>::value &&
-        // for Clang 3.5
-        !std::is_same<KeyType, detail::iter_impl<typename std::remove_const<BasicJsonType>::type>>::value;
+        !std::is_same<KeyType, typename BasicJsonType::const_iterator>::value;
 };
 
 }  // namespace detail
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 05fa0e7af..9c67db16d 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -3847,18 +3847,13 @@ decltype(ComparatorType()(std::declval<ObjectKeyType const&>(), std::declval<Key
     static constexpr bool value = true;
 };
 
-template<typename BasicJsonType>
-class iter_impl;
-
 template<typename BasicJsonType, typename KeyType>
 struct is_usable_as_key_type
 {
     static constexpr bool value =
         is_key_type_comparable<typename BasicJsonType::object_comparator_t, typename BasicJsonType::object_t::key_type, KeyType>::value &&
         !std::is_same<KeyType, typename BasicJsonType::iterator>::value &&
-        !std::is_same<KeyType, typename BasicJsonType::const_iterator>::value &&
-        // for Clang 3.5
-        !std::is_same<KeyType, detail::iter_impl<typename std::remove_const<BasicJsonType>::type>>::value;
+        !std::is_same<KeyType, typename BasicJsonType::const_iterator>::value;
 };
 
 }  // namespace detail