diff --git a/artiq/applets/plot_xy.py b/artiq/applets/plot_xy.py
index da7f2197d..8eaf9786a 100755
--- a/artiq/applets/plot_xy.py
+++ b/artiq/applets/plot_xy.py
@@ -2,6 +2,7 @@
 
 import numpy as np
 import PyQt5  # make sure pyqtgraph imports Qt5
+from PyQt5.QtCore import QTimer
 import pyqtgraph
 
 from artiq.applets.simple import TitleApplet
@@ -11,6 +12,12 @@ class XYPlot(pyqtgraph.PlotWidget):
     def __init__(self, args):
         pyqtgraph.PlotWidget.__init__(self)
         self.args = args
+        self.timer = QTimer()
+        self.timer.setSingleShot(True)
+        self.timer.timeout.connect(self.length_warning)
+        self.mismatch = {'X values': False,
+                         'Error bars': False,
+                         'Fit values': False}
 
     def data_changed(self, data, mods, title):
         try:
@@ -24,17 +31,29 @@ class XYPlot(pyqtgraph.PlotWidget):
         fit = data.get(self.args.fit, (False, None))[1]
 
         if not len(y) or len(y) != len(x):
-            return
+            self.mismatch['X values'] = True
+        else:
+            self.mismatch['X values'] = False
         if error is not None and hasattr(error, "__len__"):
             if not len(error):
                 error = None
             elif len(error) != len(y):
-                return
+                self.mismatch['Error bars'] = True
+            else:
+                self.mismatch['Error bars'] = False
         if fit is not None:
             if not len(fit):
                 fit = None
             elif len(fit) != len(y):
-                return
+                self.mismatch['Fit values'] = True
+            else:
+                self.mismatch['Fit values'] = False
+        if not any(self.mismatch.values()):
+            self.timer.stop()
+        else:
+            if not self.timer.isActive():
+                self.timer.start(1000)
+            return
 
         self.clear()
         self.plot(x, y, pen=None, symbol="x")
@@ -50,6 +69,13 @@ class XYPlot(pyqtgraph.PlotWidget):
             xi = np.argsort(x)
             self.plot(x[xi], fit[xi])
 
+    def length_warning(self):
+        self.clear()
+        text = "⚠️ dataset lengths mismatch:\n"
+        errors = ', '.join([k for k, v in self.mismatch.items() if v])
+        text = ' '.join([errors, "should have the same length as Y values"])
+        self.addItem(pyqtgraph.TextItem(text))
+
 
 def main():
     applet = TitleApplet(XYPlot)