diff --git a/format.cc b/format.cc
index 5f8a86e0..2a11fe86 100644
--- a/format.cc
+++ b/format.cc
@@ -42,6 +42,7 @@
 #include <algorithm>
 
 using std::size_t;
+using fmt::BasicFormatter;
 using fmt::Formatter;
 using fmt::FormatSpec;
 using fmt::StringRef;
@@ -135,6 +136,22 @@ void FormatDecimal(char *buffer, uint64_t value, unsigned num_digits) {
 }
 }
 
+void BasicFormatter::operator<<(int value) {
+  unsigned abs_value = value;
+  unsigned num_digits = 0;
+  char *out = 0;
+  if (value >= 0) {
+    num_digits = CountDigits(abs_value);
+    out = GrowBuffer(num_digits);
+  } else {
+    abs_value = 0 - abs_value;
+    num_digits = CountDigits(abs_value);
+    out = GrowBuffer(num_digits + 1);
+    *out++ = '-';
+  }
+  FormatDecimal(out, abs_value, num_digits);
+}
+
 // Throws Exception(message) if format contains '}', otherwise throws
 // FormatError reporting unmatched '{'. The idea is that unmatched '{'
 // should override other errors.
@@ -153,7 +170,7 @@ void Formatter::ReportError(const char *s, StringRef message) const {
 // Fills the padding around the content and returns the pointer to the
 // content area.
 char *FillPadding(char *buffer,
-    unsigned total_size, unsigned content_size, char fill) {
+    unsigned total_size, std::size_t content_size, char fill) {
   unsigned padding = total_size - content_size;
   unsigned left_padding = padding / 2;
   std::fill_n(buffer, left_padding, fill);
@@ -634,19 +651,3 @@ void Formatter::DoFormat() {
   buffer_.append(start, s + 1);
   buffer_.resize(buffer_.size() - 1);  // Don't count the terminating zero.
 }
-
-void Formatter::operator<<(int value) {
-  unsigned abs_value = value;
-  unsigned num_digits = 0;
-  char *out = 0;
-  if (value >= 0) {
-    num_digits = CountDigits(abs_value);
-    out = GrowBuffer(num_digits);
-  } else {
-    abs_value = 0 - abs_value;
-    num_digits = CountDigits(abs_value);
-    out = GrowBuffer(num_digits + 1);
-    *out++ = '-';
-  }
-  FormatDecimal(out, abs_value, num_digits);
-}
diff --git a/format.h b/format.h
index 96b45dac..8e3b7711 100644
--- a/format.h
+++ b/format.h
@@ -164,6 +164,23 @@ struct FormatSpec {
   FormatSpec() : align(ALIGN_DEFAULT), flags(0), width(0), type(0), fill(' ') {}
 };
 
+class BasicFormatter {
+ protected:
+  enum { INLINE_BUFFER_SIZE = 500 };
+  internal::Array<char, INLINE_BUFFER_SIZE> buffer_;  // Output buffer.
+
+  // Grows the buffer by n characters and returns a pointer to the newly
+  // allocated area.
+  char *GrowBuffer(std::size_t n) {
+    std::size_t size = buffer_.size();
+    buffer_.resize(size + n);
+    return &buffer_[size];
+  }
+
+ public:
+  void operator<<(int value);
+};
+
 // Formatter provides string formatting functionality similar to Python's
 // str.format. The output is stored in a memory buffer that grows dynamically.
 // Usage:
@@ -178,11 +195,7 @@ struct FormatSpec {
 //   (-3.140000, +3.140000)
 //
 // The buffer can be accessed using Formatter::data() or Formatter::c_str().
-class Formatter {
- private:
-  enum { INLINE_BUFFER_SIZE = 500 };
-  internal::Array<char, INLINE_BUFFER_SIZE> buffer_;  // Output buffer.
-
+class Formatter : public BasicFormatter {
   enum Type {
     // Numeric types should go first.
     INT, UINT, LONG, ULONG, DOUBLE, LONG_DOUBLE,
@@ -328,14 +341,6 @@ class Formatter {
     DoFormat();
   }
 
-  // Grows the buffer by n characters and returns a pointer to the newly
-  // allocated area.
-  char *GrowBuffer(std::size_t n) {
-    std::size_t size = buffer_.size();
-    buffer_.resize(size + n);
-    return &buffer_[size];
-  }
-
  public:
   Formatter() : format_(0) { buffer_[0] = 0; }
 
@@ -344,8 +349,6 @@ class Formatter {
   // using inserter operator<<.
   internal::ArgInserter operator()(const char *format);
 
-  void operator<<(int value);
-
   std::size_t size() const { return buffer_.size(); }
 
   const char *data() const { return &buffer_[0]; }