diff --git a/gtk/file_dlg_win32.c b/gtk/file_dlg_win32.c
index fbe2f64577..65f41ce9b5 100644
--- a/gtk/file_dlg_win32.c
+++ b/gtk/file_dlg_win32.c
@@ -947,7 +947,7 @@ preview_set_filename(HWND of_hwnd, gchar *preview_file) {
     TCHAR       string_buff[PREVIEW_STR_MAX];
     gint64      data_offset;
     guint       packet = 0;
-    guint64     filesize;
+    gint64      filesize;
     time_t      ti_time;
     struct tm  *ti_tm;
     guint       elapsed_time;
@@ -993,7 +993,7 @@ preview_set_filename(HWND of_hwnd, gchar *preview_file) {
 
         /* size */
         filesize = wtap_file_size(wth, &err);
-        _snwprintf(string_buff, PREVIEW_STR_MAX, _T("%") _T(PRIu64) _T(" bytes"), filesize);
+        utf_8to16_snprintf(string_buff, PREVIEW_STR_MAX, "%" G_GINT64_FORMAT " bytes", filesize);
         cur_ctrl = GetDlgItem(of_hwnd, EWFD_PTX_SIZE);
         SetWindowText(cur_ctrl, string_buff);
 
diff --git a/wsutil/libwsutil.def b/wsutil/libwsutil.def
index 4edca72000..db5d2ec498 100644
--- a/wsutil/libwsutil.def
+++ b/wsutil/libwsutil.def
@@ -47,4 +47,4 @@ type_util_guint64_to_gdouble
 ; unicode-utils.c
 utf_16to8
 utf_8to16
-
+utf_8to16_snprintf
diff --git a/wsutil/unicode-utils.c b/wsutil/unicode-utils.c
index 91c4aeca88..f011d46292 100644
--- a/wsutil/unicode-utils.c
+++ b/wsutil/unicode-utils.c
@@ -26,13 +26,8 @@
 #error "This is only for Windows"
 #endif
 
-#include <glib.h>
 #include "unicode-utils.h"
 
-#include <windows.h>
-#include <tchar.h>
-#include <wchar.h>
-
 /** @file
  * Unicode utilities (internal interface)
  *
@@ -89,6 +84,19 @@ wchar_t * utf_8to16(const char *utf8str) {
   return utf16buf[idx];
 }
 
+void utf_8to16_snprintf(TCHAR *utf16buf, gint utf16buf_len, const gchar* fmt, ...) {
+    va_list ap;
+    gchar* dst;
+
+    va_start(ap,fmt);
+    dst = g_strdup_vprintf(fmt, ap);
+    va_end(ap);
+
+    _snwprintf(utf16buf, utf16buf_len, _T("%s"), utf_8to16(dst));
+
+    g_free(dst);
+}
+
 /* Convert from UTF-16 to UTF-8. */
 gchar * utf_16to8(const wchar_t *utf16str) {
   static gchar *utf8buf[3];
diff --git a/wsutil/unicode-utils.h b/wsutil/unicode-utils.h
index 2a08be71af..f3c423ffd8 100644
--- a/wsutil/unicode-utils.h
+++ b/wsutil/unicode-utils.h
@@ -27,6 +27,15 @@
 
 #ifdef _WIN32
 
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <glib.h>
+#include <windows.h>
+#include <tchar.h>
+#include <wchar.h>
+
 /**
  * @file Unicode convenience routines.
  */
@@ -40,6 +49,14 @@
  */
 wchar_t * utf_8to16(const char *utf8str);
 
+/** Create a UTF-16 string (in place) according to the format string.
+ *
+ * @param utf16buf The buffer to return the UTF-16 string in.
+ * @param utf16buf_len The size of the 'utf16buf' parameter
+ * @param fmt A standard g_printf() format string
+ */
+void utf_8to16_snprintf(TCHAR *utf16buf, gint utf16buf_len, const gchar* fmt, ...);
+
 /** Given a UTF-16 string, convert it to UTF-8.  This is meant to be used
  * to convert between GTK+ 2.x (UTF-8) to Windows (UTF-16).
  *