diff --git a/ge/common/base64.h b/ge/common/base64.h
index bc1476ab..59661569 100644
--- a/ge/common/base64.h
+++ b/ge/common/base64.h
@@ -25,9 +25,10 @@
 
 namespace ge {
 namespace {
-const string kBase64Chars("ABCDEFGHIJKLMNOPQRSTUVWXYZ"
-                          "abcdefghijklmnopqrstuvwxyz"
-                          "0123456789+/");
+const std::string kBase64Chars = 
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+    "abcdefghijklmnopqrstuvwxyz"
+    "0123456789+/";
 const char kEqualSymbol = '=';
 const size_t kBase64CharsNum = 64;
 const size_t kThreeByteOneGroup = 3;