diff --git a/doc/conf.py b/doc/conf.py
index 6dde2bfc..93a6b17d 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -48,9 +48,9 @@ copyright = u'1990-2012, Python Software Foundation'
 # built documents.
 #
 # The short X.Y version.
-version = '0.1'
+version = '0.2'
 # The full version, including alpha/beta/rc tags.
-release = '0.1'
+release = '0.2'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
diff --git a/format.cc b/format.cc
index a6affaae..52dbe79c 100644
--- a/format.cc
+++ b/format.cc
@@ -171,8 +171,8 @@ void Formatter::ReportError(const char *s, StringRef message) const {
 // content area.
 char *FillPadding(char *buffer,
     unsigned total_size, std::size_t content_size, char fill) {
-  unsigned padding = total_size - content_size;
-  unsigned left_padding = padding / 2;
+  std::size_t padding = total_size - content_size;
+  std::size_t left_padding = padding / 2;
   std::fill_n(buffer, left_padding, fill);
   buffer += left_padding;
   char *content = buffer;
@@ -415,12 +415,26 @@ unsigned Formatter::ParseUInt(const char *&s) const {
   return value;
 }
 
-const Formatter::Arg &Formatter::ParseArgIndex(const char *&s) const {
-  if (*s < '0' || *s > '9')
-    ReportError(s, "missing argument index in format string");
-  unsigned arg_index = ParseUInt(s);
-  if (arg_index >= args_.size())
-    ReportError(s, "argument index is out of range in format");
+const Formatter::Arg &Formatter::ParseArgIndex(const char *&s) {
+  unsigned arg_index = 0;
+  if (*s < '0' || *s > '9') {
+    if (*s != '}' && *s != ':')
+      ReportError(s, "invalid argument index in format string");
+    if (next_arg_index_ < 0) {
+      ReportError(s,
+          "cannot switch from manual to automatic argument indexing");
+    }
+    arg_index = next_arg_index_++;
+  } else {
+    if (next_arg_index_ > 0) {
+      ReportError(s,
+          "cannot switch from automatic to manual argument indexing");
+    }
+    next_arg_index_ = -1;
+    arg_index = ParseUInt(s);
+    if (arg_index >= args_.size())
+      ReportError(s, "argument index is out of range in format");
+  }
   return *args_[arg_index];
 }
 
@@ -439,6 +453,7 @@ void Formatter::CheckSign(const char *&s, const Arg &arg) {
 void Formatter::DoFormat() {
   const char *start = format_;
   format_ = 0;
+  next_arg_index_ = 0;
   const char *s = start;
   while (*s) {
     char c = *s++;
diff --git a/format.h b/format.h
index 8e3b7711..f7b82567 100644
--- a/format.h
+++ b/format.h
@@ -301,6 +301,7 @@ class Formatter : public BasicFormatter {
 
   const char *format_;  // Format string.
   int num_open_braces_;
+  int next_arg_index_;
 
   friend class internal::ArgInserter;
   friend class ArgFormatter;
@@ -330,7 +331,7 @@ class Formatter : public BasicFormatter {
   unsigned ParseUInt(const char *&s) const;
 
   // Parses argument index and returns an argument with this index.
-  const Arg &ParseArgIndex(const char *&s) const;
+  const Arg &ParseArgIndex(const char *&s);
 
   void CheckSign(const char *&s, const Arg &arg);
 
diff --git a/format_test.cc b/format_test.cc
index 6660169f..4ab1e642 100644
--- a/format_test.cc
+++ b/format_test.cc
@@ -235,8 +235,8 @@ TEST(FormatterTest, ArgsInDifferentPositions) {
 
 TEST(FormatterTest, ArgErrors) {
   EXPECT_THROW_MSG(Format("{"), FormatError, "unmatched '{' in format");
-  EXPECT_THROW_MSG(Format("{}"), FormatError,
-      "missing argument index in format string");
+  EXPECT_THROW_MSG(Format("{x}"), FormatError,
+      "invalid argument index in format string");
   EXPECT_THROW_MSG(Format("{0"), FormatError, "unmatched '{' in format");
   EXPECT_THROW_MSG(Format("{0}"), FormatError,
       "argument index is out of range in format");
@@ -257,6 +257,19 @@ TEST(FormatterTest, ArgErrors) {
   EXPECT_THROW_MSG(Format(format), FormatError, "number is too big in format");
 }
 
+TEST(FormatterTest, AutoArgIndex) {
+  EXPECT_EQ("abc", str(Format("{}{}{}") << 'a' << 'b' << 'c'));
+  EXPECT_THROW_MSG(Format("{0}{}") << 'a' << 'b',
+      FormatError, "cannot switch from manual to automatic argument indexing");
+  EXPECT_THROW_MSG(Format("{}{0}") << 'a' << 'b',
+      FormatError, "cannot switch from automatic to manual argument indexing");
+  EXPECT_EQ("1.2", str(Format("{:.{}}") << 1.2345 << 2));
+  EXPECT_THROW_MSG(Format("{0}:.{}") << 1.2345 << 2,
+      FormatError, "cannot switch from manual to automatic argument indexing");
+  EXPECT_THROW_MSG(Format("{:.{0}}") << 1.2345 << 2,
+      FormatError, "cannot switch from automatic to manual argument indexing");
+}
+
 TEST(FormatterTest, EmptySpecs) {
   EXPECT_EQ("42", str(Format("{0:}") << 42));
 }
@@ -426,7 +439,6 @@ TEST(FormatterTest, SpaceSign) {
 }
 
 TEST(FormatterTest, HashFlag) {
-  // TODO
   EXPECT_EQ("42", str(Format("{0:#}") << 42));
   EXPECT_EQ("-42", str(Format("{0:#}") << -42));
   EXPECT_EQ("0x42", str(Format("{0:#x}") << 0x42));
@@ -589,8 +601,8 @@ TEST(FormatterTest, RuntimePrecision) {
       FormatError, "unmatched '{' in format");
   EXPECT_THROW_MSG(Format("{0:.{}") << 0,
       FormatError, "unmatched '{' in format");
-  EXPECT_THROW_MSG(Format("{0:.{}}") << 0,
-      FormatError, "missing argument index in format string");
+  EXPECT_THROW_MSG(Format("{0:.{x}}") << 0,
+      FormatError, "invalid argument index in format string");
   EXPECT_THROW_MSG(Format("{0:.{1}") << 0 << 0,
       FormatError, "unmatched '{' in format");
   EXPECT_THROW_MSG(Format("{0:.{1}}") << 0,