diff --git a/mainwin.py b/mainwin.py
index cdf2085..4e99ffb 100644
--- a/mainwin.py
+++ b/mainwin.py
@@ -44,6 +44,9 @@ class MainWindow(QMainWindow):
     def new_plot(self, name, cfg):
         desc = PlotDescription(**cfg)
         self.lst.add(name, desc)
+        for sub in self.mdi.subWindowList():
+            if sub.windowTitle() == name:
+                return
         self.sig_make_new_plot.emit(name, desc)