diff --git a/windows/uipriv_windows.hpp b/windows/uipriv_windows.hpp
index e207f1bc..555c687b 100644
--- a/windows/uipriv_windows.hpp
+++ b/windows/uipriv_windows.hpp
@@ -37,6 +37,7 @@ extern WCHAR *strf(const WCHAR *format, ...);
 extern WCHAR *vstrf(const WCHAR *format, va_list ap);
 extern char *LFtoCRLF(const char *lfonly);
 extern void CRLFtoLF(const char *s);
+extern WCHAR *ftoutf16(double d);
 
 // debug.cpp
 // see http://stackoverflow.com/questions/14421656/is-there-widely-available-wide-character-variant-of-file
diff --git a/windows/utf16.cpp b/windows/utf16.cpp
index 374cec9b..07fd4363 100644
--- a/windows/utf16.cpp
+++ b/windows/utf16.cpp
@@ -128,3 +128,15 @@ void CRLFtoLF(char *s)
 	while (t != s)
 		*t++ = '\0';
 }
+
+// std::to_string() always uses %f; we want %g
+// fortunately std::iostream seems to use %g by default so
+WCHAR *ftoutf16(double d)
+{
+	std::wostringstream ss;
+	std::wstring s;
+
+	ss << d;
+	s = ss.str();		// to be safe
+	return utf16dup(s.c_str());
+}