diff --git a/format.h b/format.h
index 4ad33cd6..afa1e6aa 100644
--- a/format.h
+++ b/format.h
@@ -518,7 +518,7 @@ class UTF8ToUTF16 {
   explicit UTF8ToUTF16(StringRef s);
   operator WStringRef() const { return WStringRef(&buffer_[0], size()); }
   size_t size() const { return buffer_.size() - 1; }
-  std::wstring() const { return std::wstring(&buffer_[0], size()); }
+  std::wstring str() const { return std::wstring(&buffer_[0], size()); }
 };
 
 // A converter from UTF-16 to UTF-8.
@@ -532,7 +532,7 @@ class UTF16ToUTF8 {
   explicit UTF16ToUTF8(WStringRef s);
   operator StringRef() const { return StringRef(&buffer_[0], size()); }
   size_t size() const { return buffer_.size() - 1; }
-  std::string() const { return std::string(&buffer_[0], size()); }
+  std::string str() const { return std::string(&buffer_[0], size()); }
 
   // Performs conversion returning a system error code instead of
   // throwing exception on error.