diff --git a/src/libprs500/gui2/main.py b/src/libprs500/gui2/main.py
index 38d2b600f4..0b7c6e1920 100644
--- a/src/libprs500/gui2/main.py
+++ b/src/libprs500/gui2/main.py
@@ -745,7 +745,7 @@ class Main(MainWindow, Ui_MainWindow):
     #############################View book######################################
     
     def view_format(self, row, format):
-        pt = PersistentTemporaryFile('_viewer')
+        pt = PersistentTemporaryFile('_viewer.'+format.lower())
         pt.write(self.library_view.model().db.format(row, format))
         pt.close()
         self.persistent_files.append(pt)