diff --git a/ephyviewer/epochencoder.py b/ephyviewer/epochencoder.py
index c140ce2..31ba3ba 100644
--- a/ephyviewer/epochencoder.py
+++ b/ephyviewer/epochencoder.py
@@ -89,6 +89,10 @@ def __init__(self, **kargs):
 
         self.refresh_table()
 
+        # IMPORTANT: Any time the contents of self.source are changed (e.g., by
+        # calling self.source.add_epoch), this flag must be set to True!
+        self.has_unsaved_changes = False
+
 
     def make_params(self):
         # Create parameters
@@ -298,12 +302,13 @@ def make_param_controller(self):
 
     def closeEvent(self, event):
 
-        text = 'Do you want to save epoch encoder changes before closing?'
-        title = 'Save?'
-        mb = QT.QMessageBox.question(self, title,text,
-                QT.QMessageBox.Ok ,  QT.QMessageBox.Discard)
-        if mb==QT.QMessageBox.Ok:
-            self.source.save()
+        if self.has_unsaved_changes:
+            text = 'Do you want to save epoch encoder changes before closing?'
+            title = 'Save?'
+            mb = QT.QMessageBox.question(self, title,text,
+                    QT.QMessageBox.Ok ,  QT.QMessageBox.Discard)
+            if mb==QT.QMessageBox.Ok:
+                self.source.save()
 
         self.thread.quit()
         self.thread.wait()
@@ -460,6 +465,8 @@ def on_label_shortcut(self):
         label, modifier_used = self.label_shortcuts.get(self.sender(), None)
         if label is None: return
 
+        self.has_unsaved_changes = True
+
         range_selection_is_enabled = self.but_range.isChecked()
 
         if range_selection_is_enabled:
@@ -488,6 +495,7 @@ def on_label_shortcut(self):
         self.refresh_table()
 
     def on_merge_neighbors(self):
+        self.has_unsaved_changes = True
         self.source.merge_neighbors()
         self.refresh()
         self.refresh_table()
@@ -497,6 +505,7 @@ def on_fill_blank(self):
         dia = tools.ParamDialog(params, title='Fill blank method', parent=self)
         dia.resize(300, 100)
         if dia.exec_():
+            self.has_unsaved_changes = True
             d = dia.get()
             method = d['method']
             self.source.fill_blank(method=method)
@@ -506,6 +515,7 @@ def on_fill_blank(self):
 
     def on_save(self):
         self.source.save()
+        self.has_unsaved_changes = False
 
     def on_spin_limit_changed(self, v):
         self.region.blockSignals(True)
@@ -523,6 +533,8 @@ def on_region_changed(self):
         self.spin_limit2.blockSignals(False)
 
     def apply_region(self):
+        self.has_unsaved_changes = True
+
         rgn = self.region.getRegion()
         t = rgn[0]
         duration = rgn[1] - rgn[0]
@@ -539,6 +551,8 @@ def apply_region(self):
         self.refresh_table()
 
     def delete_region(self):
+        self.has_unsaved_changes = True
+
         rgn = self.region.getRegion()
 
         self.source.delete_in_between(rgn[0], rgn[1])
@@ -628,6 +642,8 @@ def on_seek_table(self):
 
     def on_change_label(self, id, new_label):
 
+        self.has_unsaved_changes = True
+
         # get index corresponding to epoch id
         ind = self.source.id_to_ind[id]
 
@@ -642,6 +658,7 @@ def delete_selected_epoch(self):
         selected_ind = self.table_widget.selectedIndexes()
         if len(selected_ind)==0:
             return
+        self.has_unsaved_changes = True
         ind = selected_ind[0].row()
         self.source.delete_epoch(ind)
         self.refresh()
@@ -653,6 +670,7 @@ def duplicate_selected_epoch(self):
         selected_ind = self.table_widget.selectedIndexes()
         if len(selected_ind)==0:
             return
+        self.has_unsaved_changes = True
         ind = selected_ind[0].row()
         self.source.add_epoch(self.source.ep_times[ind], self.source.ep_durations[ind], self.source.ep_labels[ind])
         self.refresh()
@@ -667,6 +685,7 @@ def split_selected_epoch(self):
         ind = selected_ind[0].row()
         if self.t <= self.source.ep_times[ind] or self.source.ep_stops[ind] <= self.t:
             return
+        self.has_unsaved_changes = True
         self.source.split_epoch(ind, self.t)
         self.refresh()
         self.refresh_table()