diff --git a/doc/api.rst b/doc/api.rst
index 5a93b4aa096a..548951902693 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -120,7 +120,7 @@ custom argument formatter class::
   // A custom argument formatter that formats negative integers as unsigned
   // with the ``x`` format specifier.
   class CustomArgFormatter :
-    public fmt::BasicArgFormatter<CustomArgFormatter, char>  {
+    public fmt::BasicArgFormatter<CustomArgFormatter, char> {
     public:
     CustomArgFormatter(fmt::BasicFormatter<char, CustomArgFormatter> &f,
                        fmt::FormatSpec &s, const char *fmt)
diff --git a/fmt/format.h b/fmt/format.h
index b8713978ee1e..58b416be52ef 100644
--- a/fmt/format.h
+++ b/fmt/format.h
@@ -431,7 +431,9 @@ typedef BasicWriter<wchar_t> WWriter;
 template <typename Char>
 class ArgFormatter;
 
-template <typename Impl, typename Char>
+struct FormatSpec;
+
+template <typename Impl, typename Char, typename Spec = fmt::FormatSpec>
 class BasicPrintfArgFormatter;
 
 template <typename CharType,
@@ -1697,6 +1699,7 @@ struct TypeSpec : EmptySpec {
   int precision() const { return -1; }
   bool flag(unsigned) const { return false; }
   char type() const { return TYPE; }
+  char type_prefix() const { return TYPE; }
   char fill() const { return ' '; }
 };
 
@@ -1732,6 +1735,7 @@ struct AlignTypeSpec : AlignSpec {
 
   bool flag(unsigned) const { return false; }
   char type() const { return TYPE; }
+  char type_prefix() const { return TYPE; }
 };
 
 // A full format specifier.
@@ -1747,6 +1751,7 @@ struct FormatSpec : AlignSpec {
   bool flag(unsigned f) const { return (flags_ & f) != 0; }
   int precision() const { return precision_; }
   char type() const { return type_; }
+  char type_prefix() const { return type_; }
 };
 
 // An integer format specifier.
@@ -1922,11 +1927,11 @@ class ArgMap {
   }
 };
 
-template <typename Impl, typename Char>
+template <typename Impl, typename Char, typename Spec = fmt::FormatSpec>
 class ArgFormatterBase : public ArgVisitor<Impl, void> {
  private:
   BasicWriter<Char> &writer_;
-  FormatSpec &spec_;
+  Spec &spec_;
 
   FMT_DISALLOW_COPY_AND_ASSIGN(ArgFormatterBase);
 
@@ -1938,7 +1943,7 @@ class ArgFormatterBase : public ArgVisitor<Impl, void> {
 
  protected:
   BasicWriter<Char> &writer() { return writer_; }
-  FormatSpec &spec() { return spec_; }
+  Spec &spec() { return spec_; }
 
   void write(bool value) {
     const char *str_value = value ? "true" : "false";
@@ -1952,7 +1957,9 @@ class ArgFormatterBase : public ArgVisitor<Impl, void> {
   }
 
  public:
-  ArgFormatterBase(BasicWriter<Char> &w, FormatSpec &s)
+  typedef Spec SpecType;
+
+  ArgFormatterBase(BasicWriter<Char> &w, Spec &s)
   : writer_(w), spec_(s) {}
 
   template <typename T>
@@ -2086,8 +2093,8 @@ class FormatterBase {
   will be called.
   \endrst
  */
-template <typename Impl, typename Char>
-class BasicArgFormatter : public internal::ArgFormatterBase<Impl, Char> {
+template <typename Impl, typename Char, typename Spec = fmt::FormatSpec>
+class BasicArgFormatter : public internal::ArgFormatterBase<Impl, Char, Spec> {
  private:
   BasicFormatter<Char, Impl> &formatter_;
   const Char *format_;
@@ -2102,8 +2109,8 @@ class BasicArgFormatter : public internal::ArgFormatterBase<Impl, Char> {
     \endrst
    */
   BasicArgFormatter(BasicFormatter<Char, Impl> &formatter,
-                    FormatSpec &spec, const Char *fmt)
-  : internal::ArgFormatterBase<Impl, Char>(formatter.writer(), spec),
+                    Spec &spec, const Char *fmt)
+  : internal::ArgFormatterBase<Impl, Char, Spec>(formatter.writer(), spec),
     formatter_(formatter), format_(fmt) {}
 
   /** Formats an argument of a custom (user-defined) type. */
@@ -2114,12 +2121,14 @@ class BasicArgFormatter : public internal::ArgFormatterBase<Impl, Char> {
 
 /** The default argument formatter. */
 template <typename Char>
-class ArgFormatter : public BasicArgFormatter<ArgFormatter<Char>, Char> {
+class ArgFormatter :
+    public BasicArgFormatter<ArgFormatter<Char>, Char, FormatSpec> {
  public:
   /** Constructs an argument formatter object. */
   ArgFormatter(BasicFormatter<Char> &formatter,
                FormatSpec &spec, const Char *fmt)
-  : BasicArgFormatter<ArgFormatter<Char>, Char>(formatter, spec, fmt) {}
+  : BasicArgFormatter<ArgFormatter<Char>,
+                      Char, FormatSpec>(formatter, spec, fmt) {}
 };
 
 /** This template formats data and writes the output to a writer. */
@@ -2501,16 +2510,16 @@ class BasicWriter {
   void write_int(T value, Spec spec);
 
   // Formats a floating-point number (double or long double).
-  template <typename T>
-  void write_double(T value, const FormatSpec &spec);
+  template <typename T, typename Spec>
+  void write_double(T value, const Spec &spec);
 
   // Writes a formatted string.
   template <typename StrChar>
   CharPtr write_str(const StrChar *s, std::size_t size, const AlignSpec &spec);
 
-  template <typename StrChar>
+  template <typename StrChar, typename Spec>
   void write_str(const internal::Arg::StringValue<StrChar> &str,
-                 const FormatSpec &spec);
+                 const Spec &spec);
 
   // This following methods are private to disallow writing wide characters
   // and strings to a char stream. If you want to print a wide string as a
@@ -2529,10 +2538,10 @@ class BasicWriter {
   template<typename T>
   void append_float_length(Char *&, T) {}
 
-  template <typename Impl, typename Char_>
+  template <typename Impl, typename Char_, typename Spec_>
   friend class internal::ArgFormatterBase;
 
-  template <typename Impl, typename Char_>
+  template <typename Impl, typename Char_, typename Spec_>
   friend class BasicPrintfArgFormatter;
 
  protected:
@@ -2729,9 +2738,9 @@ typename BasicWriter<Char>::CharPtr BasicWriter<Char>::write_str(
 }
 
 template <typename Char>
-template <typename StrChar>
+template <typename StrChar, typename Spec>
 void BasicWriter<Char>::write_str(
-    const internal::Arg::StringValue<StrChar> &s, const FormatSpec &spec) {
+    const internal::Arg::StringValue<StrChar> &s, const Spec &spec) {
   // Check if StrChar is convertible to Char.
   internal::CharTraits<Char>::convert(StrChar());
   if (spec.type_ && spec.type_ != 's')
@@ -2855,7 +2864,7 @@ void BasicWriter<Char>::write_int(T value, Spec spec) {
     UnsignedType n = abs_value;
     if (spec.flag(HASH_FLAG)) {
       prefix[prefix_size++] = '0';
-      prefix[prefix_size++] = spec.type();
+      prefix[prefix_size++] = spec.type_prefix();
     }
     unsigned num_digits = 0;
     do {
@@ -2875,7 +2884,7 @@ void BasicWriter<Char>::write_int(T value, Spec spec) {
     UnsignedType n = abs_value;
     if (spec.flag(HASH_FLAG)) {
       prefix[prefix_size++] = '0';
-      prefix[prefix_size++] = spec.type();
+      prefix[prefix_size++] = spec.type_prefix();
     }
     unsigned num_digits = 0;
     do {
@@ -2923,8 +2932,8 @@ void BasicWriter<Char>::write_int(T value, Spec spec) {
 }
 
 template <typename Char>
-template <typename T>
-void BasicWriter<Char>::write_double(T value, const FormatSpec &spec) {
+template <typename T, typename Spec>
+void BasicWriter<Char>::write_double(T value, const Spec &spec) {
   // Check type.
   char type = spec.type();
   bool upper = false;
@@ -3661,7 +3670,7 @@ const Char *BasicFormatter<Char, ArgFormatter>::format(
     const Char *&format_str, const internal::Arg &arg) {
   using internal::Arg;
   const Char *s = format_str;
-  FormatSpec spec;
+  typename ArgFormatter::SpecType spec;
   if (*s == ':') {
     if (arg.type == Arg::CUSTOM) {
       arg.custom.format(this, arg.custom.value, &s);
diff --git a/fmt/printf.h b/fmt/printf.h
index 80d224417ace..28f32f8e7779 100644
--- a/fmt/printf.h
+++ b/fmt/printf.h
@@ -189,15 +189,16 @@ class WidthHandler : public ArgVisitor<WidthHandler, unsigned> {
   superclass will be called.
   \endrst
  */
-template <typename Impl, typename Char>
-class BasicPrintfArgFormatter : public internal::ArgFormatterBase<Impl, Char> {
+template <typename Impl, typename Char, typename Spec>
+class BasicPrintfArgFormatter :
+    public internal::ArgFormatterBase<Impl, Char, Spec> {
  private:
   void write_null_pointer() {
     this->spec().type_ = 0;
     this->write("(nil)");
   }
 
-  typedef internal::ArgFormatterBase<Impl, Char> Base;
+  typedef internal::ArgFormatterBase<Impl, Char, Spec> Base;
 
  public:
   /**
@@ -207,12 +208,12 @@ class BasicPrintfArgFormatter : public internal::ArgFormatterBase<Impl, Char> {
     specifier information for standard argument types.
     \endrst
    */
-  BasicPrintfArgFormatter(BasicWriter<Char> &w, FormatSpec &s)
-  : internal::ArgFormatterBase<Impl, Char>(w, s) {}
+  BasicPrintfArgFormatter(BasicWriter<Char> &w, Spec &s)
+  : internal::ArgFormatterBase<Impl, Char, Spec>(w, s) {}
 
   /** Formats an argument of type ``bool``. */
   void visit_bool(bool value) {
-    FormatSpec &fmt_spec = this->spec();
+    Spec &fmt_spec = this->spec();
     if (fmt_spec.type_ != 's')
       return this->visit_any_int(value);
     fmt_spec.type_ = 0;
@@ -221,7 +222,7 @@ class BasicPrintfArgFormatter : public internal::ArgFormatterBase<Impl, Char> {
 
   /** Formats a character. */
   void visit_char(int value) {
-    const FormatSpec &fmt_spec = this->spec();
+    const Spec &fmt_spec = this->spec();
     BasicWriter<Char> &w = this->writer();
     if (fmt_spec.type_ && fmt_spec.type_ != 'c')
       w.write_int(value, fmt_spec);
@@ -271,12 +272,12 @@ class BasicPrintfArgFormatter : public internal::ArgFormatterBase<Impl, Char> {
 
 /** The default printf argument formatter. */
 template <typename Char>
-class PrintfArgFormatter
-    : public BasicPrintfArgFormatter<PrintfArgFormatter<Char>, Char> {
+class PrintfArgFormatter :
+    public BasicPrintfArgFormatter<PrintfArgFormatter<Char>, Char, FormatSpec> {
  public:
   /** Constructs an argument formatter object. */
   PrintfArgFormatter(BasicWriter<Char> &w, FormatSpec &s)
-  : BasicPrintfArgFormatter<PrintfArgFormatter<Char>, Char>(w, s) {}
+  : BasicPrintfArgFormatter<PrintfArgFormatter<Char>, Char, FormatSpec>(w, s) {}
 };
 
 /** This template formats data and writes the output to a writer. */
diff --git a/test/custom-formatter-test.cc b/test/custom-formatter-test.cc
index cc9c44854b50..0b573841265b 100644
--- a/test/custom-formatter-test.cc
+++ b/test/custom-formatter-test.cc
@@ -30,8 +30,8 @@ class CustomArgFormatter
 
 // A custom argument formatter that doesn't print `-` for floating-point values
 // rounded to 0.
-class CustomPrintfArgFormatter :
-    public BasicPrintfArgFormatter<CustomPrintfArgFormatter, char> {
+class CustomPrintfArgFormatter
+  : public BasicPrintfArgFormatter<CustomPrintfArgFormatter, char> {
  public:
   typedef BasicPrintfArgFormatter<CustomPrintfArgFormatter, char> Base;
 
diff --git a/test/format-test.cc b/test/format-test.cc
index c812b067bd35..6d4a8fcd22b1 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -1660,4 +1660,3 @@ void convert(int);
 TEST(FormatTest, ConvertCollision) {
   fmt::format("{}", 42);
 }
-