diff --git a/CMakeLists.txt b/CMakeLists.txt
index 06e6e7b0..684f8149 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -69,7 +69,7 @@ endif ()
 add_library(format ${shared} ${FMT_SOURCES})
 if (CMAKE_COMPILER_IS_GNUCXX)
   set_target_properties(format PROPERTIES COMPILE_FLAGS
-    "-Wall -Wextra -pedantic")
+    "-Wall -Wextra -Wshadow -pedantic")
 endif ()
 if (CPP11_FLAG AND FMT_EXTRA_TESTS)
   set_target_properties(format PROPERTIES COMPILE_FLAGS ${CPP11_FLAG})
diff --git a/format.cc b/format.cc
index 81a2ede0..07ce60b7 100644
--- a/format.cc
+++ b/format.cc
@@ -362,10 +362,10 @@ inline Arg::StringValue<wchar_t> ignore_incompatible_str(
 }  // namespace
 
 FMT_FUNC void fmt::SystemError::init(
-    int error_code, StringRef format_str, ArgList args) {
-  error_code_ = error_code;
+    int err_code, StringRef format_str, ArgList args) {
+  error_code_ = err_code;
   MemoryWriter w;
-  internal::format_system_error(w, error_code, format(format_str, args));
+  internal::format_system_error(w, err_code, format(format_str, args));
   std::runtime_error &base = *this;
   base = std::runtime_error(w.str());
 }
@@ -612,20 +612,20 @@ class fmt::internal::ArgFormatter :
 template <typename Char>
 template <typename StrChar>
 void fmt::BasicWriter<Char>::write_str(
-    const Arg::StringValue<StrChar> &str, const FormatSpec &spec) {
+    const Arg::StringValue<StrChar> &s, const FormatSpec &spec) {
   // Check if StrChar is convertible to Char.
   internal::CharTraits<Char>::convert(StrChar());
   if (spec.type_ && spec.type_ != 's')
     internal::report_unknown_type(spec.type_, "string");
-  const StrChar *s = str.value;
-  std::size_t size = str.size;
-  if (size == 0) {
-    if (!s)
+  const StrChar *str_value = s.value;
+  std::size_t str_size = s.size;
+  if (str_size == 0) {
+    if (!str_value)
       FMT_THROW(FormatError("string pointer is null"));
-    if (*s)
-      size = std::char_traits<StrChar>::length(s);
+    if (*str_value)
+      str_size = std::char_traits<StrChar>::length(str_value);
   }
-  write_str(s, size, spec);
+  write_str(str_value, str_size, spec);
 }
 
 template <typename Char>
@@ -739,9 +739,9 @@ unsigned fmt::internal::PrintfFormatter<Char>::parse_header(
 
 template <typename Char>
 void fmt::internal::PrintfFormatter<Char>::format(
-    BasicWriter<Char> &writer, BasicStringRef<Char> format,
+    BasicWriter<Char> &writer, BasicStringRef<Char> format_str,
     const ArgList &args) {
-  const Char *start = format.c_str();
+  const Char *start = format_str.c_str();
   set_args(args);
   const Char *s = start;
   while (*s) {
@@ -892,8 +892,8 @@ void fmt::internal::PrintfFormatter<Char>::format(
     case Arg::CUSTOM: {
       if (spec.type_)
         internal::report_unknown_type(spec.type_, "object");
-      const void *s = "s";
-      arg.custom.format(&writer, arg.custom.value, &s);
+      const void *str_format = "s";
+      arg.custom.format(&writer, arg.custom.value, &str_format);
       break;
     }
     default:
diff --git a/format.h b/format.h
index c3c2d876..7c871acd 100644
--- a/format.h
+++ b/format.h
@@ -47,11 +47,14 @@
 #ifdef __GNUC__
 # define FMT_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__)
 # define FMT_GCC_EXTENSION __extension__
-// Disable warning about "long long" which is sometimes reported even
-// when using __extension__.
 # if FMT_GCC_VERSION >= 406
 #  pragma GCC diagnostic push
+// Disable the warning about "long long" which is sometimes reported even
+// when using __extension__.
 #  pragma GCC diagnostic ignored "-Wlong-long"
+// Disable the warning about declaration shadowing because it affects too
+// many valid cases.
+#  pragma GCC diagnostic ignored "-Wshadow"
 # endif
 #else
 # define FMT_GCC_EXTENSION
@@ -154,7 +157,7 @@ void format(BasicFormatter<Char> &f, const Char *&format_str, const T &value);
   different types of strings to a function, for example::
 
     template <typename... Args>
-    std::string format(StringRef format, const Args & ... args);
+    std::string format(StringRef format_str, const Args & ... args);
 
     format("{}", 42);
     format(std::string("{}"), 42);
@@ -989,7 +992,7 @@ class PrintfFormatter : private FormatterBase {
 
  public:
   void format(BasicWriter<Char> &writer,
-    BasicStringRef<Char> format, const ArgList &args);
+    BasicStringRef<Char> format_str, const ArgList &args);
 };
 }  // namespace internal
 
@@ -1388,7 +1391,7 @@ inline uint64_t make_type(FMT_GEN15(FMT_ARG_TYPE_DEFAULT)) {
 */
 class SystemError : public internal::RuntimeError {
  private:
-  void init(int error_code, StringRef format_str, ArgList args);
+  void init(int err_code, StringRef format_str, ArgList args);
 
  protected:
   int error_code_;