diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index c1cd8bbb..031bdac2 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -59,7 +59,7 @@ CHECK_CXX_COMPILER_FLAG("-Wuseless-cast"        COMPILER_SUPPORTS_WUSELESS_CAST)
 CHECK_CXX_COMPILER_FLAG("-Wdouble-promotion"    COMPILER_SUPPORTS_WDOUBLE_PROMOTION)
 CHECK_CXX_COMPILER_FLAG("-Wrange-loop-analysis" COMPILER_SUPPORTS_WRANGE_LOOP_ANALYSIS)
 CHECK_CXX_COMPILER_FLAG("-Wundef"               COMPILER_SUPPORTS_WUNDEF)
-CHECK_CXX_COMPILER_FLAG("-Wshadow=local"        COMPILER_SUPPORTS_WSHADOW_LOCAL)
+CHECK_CXX_COMPILER_FLAG("-Wshadow"              COMPILER_SUPPORTS_WSHADOW)
 
 if(COMPILER_SUPPORTS_WALL)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall")
@@ -73,8 +73,8 @@ endif()
 if(COMPILER_SUPPORTS_WERROR)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
 endif()
-if(COMPILER_SUPPORTS_WSHADOW_LOCAL)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wshadow=local")
+if(COMPILER_SUPPORTS_WSHADOW)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wshadow")
 endif()
 if(COMPILER_SUPPORTS_WSIGN_CONVERSION)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wsign-conversion")
diff --git a/toml/region.hpp b/toml/region.hpp
index 37ba3a30..2e01e51d 100644
--- a/toml/region.hpp
+++ b/toml/region.hpp
@@ -73,13 +73,13 @@ struct location final : public region_base
     using difference_type = typename const_iterator::difference_type;
     using source_ptr      = std::shared_ptr<const std::vector<char>>;
 
-    location(std::string name, std::vector<char> cont)
+    location(std::string source_name, std::vector<char> cont)
       : source_(std::make_shared<std::vector<char>>(std::move(cont))),
-        line_number_(1), source_name_(std::move(name)), iter_(source_->cbegin())
+        line_number_(1), source_name_(std::move(source_name)), iter_(source_->cbegin())
     {}
-    location(std::string name, const std::string& cont)
+    location(std::string source_name, const std::string& cont)
       : source_(std::make_shared<std::vector<char>>(cont.begin(), cont.end())),
-        line_number_(1), source_name_(std::move(name)), iter_(source_->cbegin())
+        line_number_(1), source_name_(std::move(source_name)), iter_(source_->cbegin())
     {}
 
     location(const location&) = default;
@@ -343,9 +343,9 @@ struct region final : public region_base
                             }))
                     {
                         // unwrap the first '#' by std::next.
-                        auto str = make_string(std::next(comment_found), iter);
-                        if(!str.empty() && str.back() == '\r') {str.pop_back();}
-                        com.push_back(std::move(str));
+                        auto s = make_string(std::next(comment_found), iter);
+                        if(!s.empty() && s.back() == '\r') {s.pop_back();}
+                        com.push_back(std::move(s));
                     }
                     else
                     {
@@ -396,9 +396,9 @@ struct region final : public region_base
                     }))
                 {
                     // unwrap the first '#' by std::next.
-                    auto str = make_string(std::next(comment_found), this->line_end());
-                    if(!str.empty() && str.back() == '\r') {str.pop_back();}
-                    com.push_back(std::move(str));
+                    auto s = make_string(std::next(comment_found), this->line_end());
+                    if(!s.empty() && s.back() == '\r') {s.pop_back();}
+                    com.push_back(std::move(s));
                 }
             }
         }
diff --git a/toml/serializer.hpp b/toml/serializer.hpp
index 77aef589..b27abfd9 100644
--- a/toml/serializer.hpp
+++ b/toml/serializer.hpp
@@ -26,19 +26,19 @@ namespace toml
 // a `"` and escaping some special character is boring.
 template<typename charT, typename traits, typename Alloc>
 std::basic_string<charT, traits, Alloc>
-format_key(const std::basic_string<charT, traits, Alloc>& key)
+format_key(const std::basic_string<charT, traits, Alloc>& k)
 {
     // check the key can be a bare (unquoted) key
-    detail::location loc(key, std::vector<char>(key.begin(), key.end()));
+    detail::location loc(k, std::vector<char>(k.begin(), k.end()));
     detail::lex_unquoted_key::invoke(loc);
     if(loc.iter() == loc.end())
     {
-        return key; // all the tokens are consumed. the key is unquoted-key.
+        return k; // all the tokens are consumed. the key is unquoted-key.
     }
 
     //if it includes special characters, then format it in a "quoted" key.
     std::basic_string<charT, traits, Alloc> serialized("\"");
-    for(const char c : key)
+    for(const char c : k)
     {
         switch(c)
         {
diff --git a/toml/types.hpp b/toml/types.hpp
index 0818ebd1..7bf4b2e8 100644
--- a/toml/types.hpp
+++ b/toml/types.hpp
@@ -21,6 +21,11 @@ class basic_value;
 using character = char;
 using key = std::string;
 
+#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ <= 4
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wshadow"
+#endif
+
 using boolean        = bool;
 using integer        = std::int64_t;
 using floating       = double; // "float" is a keyward, cannot use it here.
@@ -32,12 +37,26 @@ using floating       = double; // "float" is a keyward, cannot use it here.
 // - local_date
 // - local_time
 
+#if defined(__GNUC__) && !defined(__clang__)
+#  pragma GCC diagnostic pop
+#endif
+
 // default toml::value and default array/table. these are defined after defining
 // basic_value itself.
 // using value = basic_value<discard_comments, std::unordered_map, std::vector>;
 // using array = typename value::array_type;
 // using table = typename value::table_type;
 
+// to avoid warnings about `value_t::integer` is "shadowing" toml::integer in
+// GCC -Wshadow=global.
+#if defined(__GNUC__) && !defined(__clang__)
+#  pragma GCC diagnostic push
+#  if 7 <= __GNUC__
+#    pragma GCC diagnostic ignored "-Wshadow=global"
+#  else // gcc-6 or older
+#    pragma GCC diagnostic ignored "-Wshadow"
+#  endif
+#endif
 enum class value_t : std::uint8_t
 {
     empty           =  0,
@@ -52,6 +71,9 @@ enum class value_t : std::uint8_t
     array           =  9,
     table           = 10,
 };
+#if defined(__GNUC__) && !defined(__clang__)
+#  pragma GCC diagnostic pop
+#endif
 
 template<typename charT, typename traits>
 inline std::basic_ostream<charT, traits>&
@@ -147,4 +169,5 @@ template<typename T, typename V> struct is_exact_toml_type<T const volatile&, V>
 
 } // detail
 } // toml
+
 #endif// TOML11_TYPES_H
diff --git a/toml/value.hpp b/toml/value.hpp
index f2e6c635..ed8c76e3 100644
--- a/toml/value.hpp
+++ b/toml/value.hpp
@@ -281,9 +281,9 @@ class basic_value
 
     // overwrite comments ----------------------------------------------------
 
-    basic_value(const basic_value& v, std::vector<std::string> comments)
+    basic_value(const basic_value& v, std::vector<std::string> com)
         : type_(v.type()), region_info_(v.region_info_),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         switch(v.type())
         {
@@ -301,9 +301,9 @@ class basic_value
         }
     }
 
-    basic_value(basic_value&& v, std::vector<std::string> comments)
+    basic_value(basic_value&& v, std::vector<std::string> com)
         : type_(v.type()), region_info_(std::move(v.region_info_)),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         switch(this->type_) // here this->type_ is already initialized
         {
@@ -359,9 +359,9 @@ class basic_value
     template<typename C,
              template<typename ...> class T,
              template<typename ...> class A>
-    basic_value(const basic_value<C, T, A>& v, std::vector<std::string> comments)
+    basic_value(const basic_value<C, T, A>& v, std::vector<std::string> com)
         : type_(v.type()), region_info_(v.region_info_),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         switch(v.type())
         {
@@ -443,10 +443,10 @@ class basic_value
         assigner(this->boolean_, b);
         return *this;
     }
-    basic_value(boolean b, std::vector<std::string> comments)
+    basic_value(boolean b, std::vector<std::string> com)
         : type_(value_t::boolean),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->boolean_, b);
     }
@@ -478,10 +478,10 @@ class basic_value
     template<typename T, typename std::enable_if<detail::conjunction<
         std::is_integral<T>, detail::negation<std::is_same<T, boolean>>>::value,
         std::nullptr_t>::type = nullptr>
-    basic_value(T i, std::vector<std::string> comments)
+    basic_value(T i, std::vector<std::string> com)
         : type_(value_t::integer),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->integer_, static_cast<integer>(i));
     }
@@ -511,10 +511,10 @@ class basic_value
 
     template<typename T, typename std::enable_if<
         std::is_floating_point<T>::value, std::nullptr_t>::type = nullptr>
-    basic_value(T f, std::vector<std::string> comments)
+    basic_value(T f, std::vector<std::string> com)
         : type_(value_t::floating),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->floating_, f);
     }
@@ -535,10 +535,10 @@ class basic_value
         assigner(this->string_, s);
         return *this;
     }
-    basic_value(toml::string s, std::vector<std::string> comments)
+    basic_value(toml::string s, std::vector<std::string> com)
         : type_(value_t::string),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->string_, std::move(s));
     }
@@ -563,17 +563,17 @@ class basic_value
     {
         assigner(this->string_, toml::string(std::move(s), kind));
     }
-    basic_value(std::string s, std::vector<std::string> comments)
+    basic_value(std::string s, std::vector<std::string> com)
         : type_(value_t::string),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->string_, toml::string(std::move(s)));
     }
-    basic_value(std::string s, string_t kind, std::vector<std::string> comments)
+    basic_value(std::string s, string_t kind, std::vector<std::string> com)
         : type_(value_t::string),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->string_, toml::string(std::move(s), kind));
     }
@@ -598,17 +598,17 @@ class basic_value
     {
         assigner(this->string_, toml::string(std::string(s), kind));
     }
-    basic_value(const char* s, std::vector<std::string> comments)
+    basic_value(const char* s, std::vector<std::string> com)
         : type_(value_t::string),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->string_, toml::string(std::string(s)));
     }
-    basic_value(const char* s, string_t kind, std::vector<std::string> comments)
+    basic_value(const char* s, string_t kind, std::vector<std::string> com)
         : type_(value_t::string),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->string_, toml::string(std::string(s), kind));
     }
@@ -628,10 +628,10 @@ class basic_value
         assigner(this->string_, toml::string(s));
         return *this;
     }
-    basic_value(std::string_view s, std::vector<std::string> comments)
+    basic_value(std::string_view s, std::vector<std::string> com)
         : type_(value_t::string),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->string_, toml::string(s));
     }
@@ -641,10 +641,10 @@ class basic_value
     {
         assigner(this->string_, toml::string(s, kind));
     }
-    basic_value(std::string_view s, string_t kind, std::vector<std::string> comments)
+    basic_value(std::string_view s, string_t kind, std::vector<std::string> com)
         : type_(value_t::string),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->string_, toml::string(s, kind));
     }
@@ -666,10 +666,10 @@ class basic_value
         assigner(this->local_date_, ld);
         return *this;
     }
-    basic_value(const local_date& ld, std::vector<std::string> comments)
+    basic_value(const local_date& ld, std::vector<std::string> com)
         : type_(value_t::local_date),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->local_date_, ld);
     }
@@ -682,10 +682,10 @@ class basic_value
     {
         assigner(this->local_time_, lt);
     }
-    basic_value(const local_time& lt, std::vector<std::string> comments)
+    basic_value(const local_time& lt, std::vector<std::string> com)
         : type_(value_t::local_time),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->local_time_, lt);
     }
@@ -707,10 +707,10 @@ class basic_value
     }
     template<typename Rep, typename Period>
     basic_value(const std::chrono::duration<Rep, Period>& dur,
-                std::vector<std::string> comments)
+                std::vector<std::string> com)
         : type_(value_t::local_time),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->local_time_, local_time(dur));
     }
@@ -732,10 +732,10 @@ class basic_value
     {
         assigner(this->local_datetime_, ldt);
     }
-    basic_value(const local_datetime& ldt, std::vector<std::string> comments)
+    basic_value(const local_datetime& ldt, std::vector<std::string> com)
         : type_(value_t::local_datetime),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->local_datetime_, ldt);
     }
@@ -756,10 +756,10 @@ class basic_value
     {
         assigner(this->offset_datetime_, odt);
     }
-    basic_value(const offset_datetime& odt, std::vector<std::string> comments)
+    basic_value(const offset_datetime& odt, std::vector<std::string> com)
         : type_(value_t::offset_datetime),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->offset_datetime_, odt);
     }
@@ -778,10 +778,10 @@ class basic_value
         assigner(this->offset_datetime_, offset_datetime(tp));
     }
     basic_value(const std::chrono::system_clock::time_point& tp,
-                std::vector<std::string> comments)
+                std::vector<std::string> com)
         : type_(value_t::offset_datetime),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->offset_datetime_, offset_datetime(tp));
     }
@@ -802,10 +802,10 @@ class basic_value
     {
         assigner(this->array_, ary);
     }
-    basic_value(const array_type& ary, std::vector<std::string> comments)
+    basic_value(const array_type& ary, std::vector<std::string> com)
         : type_(value_t::array),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->array_, ary);
     }
@@ -833,10 +833,10 @@ class basic_value
     template<typename T, typename std::enable_if<
             std::is_convertible<T, value_type>::value,
         std::nullptr_t>::type = nullptr>
-    basic_value(std::initializer_list<T> list, std::vector<std::string> comments)
+    basic_value(std::initializer_list<T> list, std::vector<std::string> com)
         : type_(value_t::array),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         array_type ary(list.begin(), list.end());
         assigner(this->array_, std::move(ary));
@@ -876,10 +876,10 @@ class basic_value
             detail::negation<std::is_same<T, array_type>>,
             detail::is_container<T>
         >::value, std::nullptr_t>::type = nullptr>
-    basic_value(const T& list, std::vector<std::string> comments)
+    basic_value(const T& list, std::vector<std::string> com)
         : type_(value_t::array),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         static_assert(std::is_convertible<typename T::value_type, value_type>::value,
             "elements of a container should be convertible to toml::value");
@@ -915,10 +915,10 @@ class basic_value
     {
         assigner(this->table_, tab);
     }
-    basic_value(const table_type& tab, std::vector<std::string> comments)
+    basic_value(const table_type& tab, std::vector<std::string> com)
         : type_(value_t::table),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         assigner(this->table_, tab);
     }
@@ -943,10 +943,10 @@ class basic_value
     }
 
     basic_value(std::initializer_list<std::pair<key, basic_value>> list,
-                std::vector<std::string> comments)
+                std::vector<std::string> com)
         : type_(value_t::table),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         table_type tab;
         for(const auto& elem : list) {tab[elem.first] = elem.second;}
@@ -982,10 +982,10 @@ class basic_value
             detail::negation<std::is_same<Map, table_type>>,
             detail::is_map<Map>
         >::value, std::nullptr_t>::type = nullptr>
-    basic_value(const Map& mp, std::vector<std::string> comments)
+    basic_value(const Map& mp, std::vector<std::string> com)
         : type_(value_t::table),
           region_info_(std::make_shared<region_base>(region_base{})),
-          comments_(std::move(comments))
+          comments_(std::move(com))
     {
         table_type tab;
         for(const auto& elem : mp) {tab[elem.first] = elem.second;}
@@ -1017,8 +1017,8 @@ class basic_value
 
     template<typename T, typename std::enable_if<
         detail::has_into_toml_method<T>::value, std::nullptr_t>::type = nullptr>
-    basic_value(const T& ud, std::vector<std::string> comments)
-        : basic_value(ud.into_toml(), std::move(comments))
+    basic_value(const T& ud, std::vector<std::string> com)
+        : basic_value(ud.into_toml(), std::move(com))
     {}
     template<typename T, typename std::enable_if<
         detail::has_into_toml_method<T>::value, std::nullptr_t>::type = nullptr>
@@ -1033,8 +1033,8 @@ class basic_value
     template<typename T, std::size_t S = sizeof(::toml::into<T>)>
     basic_value(const T& ud): basic_value(::toml::into<T>::into_toml(ud)) {}
     template<typename T, std::size_t S = sizeof(::toml::into<T>)>
-    basic_value(const T& ud, std::vector<std::string> comments)
-        : basic_value(::toml::into<T>::into_toml(ud), std::move(comments))
+    basic_value(const T& ud, std::vector<std::string> com)
+        : basic_value(::toml::into<T>::into_toml(ud), std::move(com))
     {}
     template<typename T, std::size_t S = sizeof(::toml::into<T>)>
     basic_value& operator=(const T& ud)
@@ -1134,10 +1134,10 @@ class basic_value
     template<typename T, typename std::enable_if<
         detail::is_exact_toml_type<T, value_type>::value,
         std::nullptr_t>::type = nullptr>
-    basic_value(std::pair<T, detail::region> parse_result, std::vector<std::string> comments)
+    basic_value(std::pair<T, detail::region> parse_result, std::vector<std::string> com)
         : basic_value(std::move(parse_result.first),
                       std::move(parse_result.second),
-                      std::move(comments))
+                      std::move(com))
     {}
 
     // type checking and casting ============================================