diff --git a/src/base/string_piece.h b/src/base/string_piece.h
index 6355dc1..097163b 100644
--- a/src/base/string_piece.h
+++ b/src/base/string_piece.h
@@ -116,6 +116,10 @@
     return string(!empty() ? data() : "", size());
   }
 
+  explicit operator string() const {
+    return string(!empty() ? data() : "", size());
+  }
+
   void CopyToString(string *target) const;
   void AppendToString(string *target) const;
 
diff --git a/src/base/string_piece_test.cc b/src/base/string_piece_test.cc
index 2d70b7e..1900be2 100644
--- a/src/base/string_piece_test.cc
+++ b/src/base/string_piece_test.cc
@@ -503,6 +503,16 @@
   ASSERT_EQ(c, s3);
   string s4(e.as_string());
   ASSERT_TRUE(s4.empty());
+
+  // cast to string
+  c = StringPiece("foobar");
+  ASSERT_EQ(string("foobar"), string(c));
+  c = StringPiece("foobar", 6);
+  ASSERT_EQ(string("foobar"), string(c));
+  c = StringPiece("foobarfoobar", 6);
+  ASSERT_EQ(string("foobar"), string(c));
+  string s5 = string(e);
+  ASSERT_TRUE(s5.empty());
 }
 
 TEST(StringPieceTest, CheckNULL) {
diff --git a/src/data/version/mozc_version_template.bzl b/src/data/version/mozc_version_template.bzl
index 0a0145e..8e150ff 100644
--- a/src/data/version/mozc_version_template.bzl
+++ b/src/data/version/mozc_version_template.bzl
@@ -30,7 +30,7 @@
 
 MAJOR=2
 MINOR=21
-BUILD=2708
+BUILD=2709
 REVISION=102
 # This version represents the version of Mozc IME engine (converter, predictor,
 # etc.).  This version info is included both in the Mozc server and in the Mozc