diff --git a/src/modalWindows.py b/src/modalWindows.py
index c9df839..ef18232 100644
--- a/src/modalWindows.py
+++ b/src/modalWindows.py
@@ -1860,7 +1860,7 @@ def __init__(self, master=None,controller=None,initialValue='',videoDuration=0,
     self.entryTimestamps.grid(row=1,column=0,sticky='new',padx=5,pady=5)
     self.varTimestamps.trace('w',self.valueUpdated)
 
-    self.varnegativeTS = tk.IntVar(0)
+    self.varnegativeTS = tk.IntVar(self,0)
     self.checknegativeTS =  ttk.Checkbutton(self,text='Interpret as negative timestamps from end of clip.',var=self.varnegativeTS)
     self.checknegativeTS.grid(row=2,column=0,sticky='new',padx=5,pady=5)
     self.varnegativeTS.trace('w',self.valueUpdated)
@@ -2536,4 +2536,4 @@ def valueChanged(self,valueKey):
 
 if __name__ == "__main__":
   app = AdvancedEncodeFlagsModal()
-  app.mainloop()
\ No newline at end of file
+  app.mainloop()