diff --git a/src/calibre/gui2/metadata/diff.py b/src/calibre/gui2/metadata/diff.py
index f3bfda3a32..ad9c5d42fc 100644
--- a/src/calibre/gui2/metadata/diff.py
+++ b/src/calibre/gui2/metadata/diff.py
@@ -93,6 +93,11 @@ class LineEdit(EditWithComplete):
         self.setText(val)
         self.setCursorPosition(0)
 
+    def set_undoable(self, val):
+        self.selectAll()
+        self.insert(val)
+        self.setCursorPosition(0)
+
     @property
     def is_blank(self):
         val = self.current_val.strip()
@@ -138,6 +143,9 @@ class LanguagesEdit(LE):
     def same_as(self, other):
         return self.current_val == other.current_val
 
+    def set_undoable(self, val):
+        self.set_lang_codes(val, True)
+
 
 class RatingsEdit(RatingEdit):
 
@@ -191,6 +199,9 @@ class DateEdit(PubdateEdit):
     def same_as(self, other):
         return self.text() == other.text()
 
+    def set_undoable(self, val):
+        self.set_value(val)
+
 
 class SeriesEdit(LineEdit):
 
@@ -274,6 +285,10 @@ class CommentsEdit(Editor):
         self.html = val or ''
         self.changed.emit()
 
+    def set_undoable(self, val):
+        self.set_html(val, allow_undo=True)
+        self.changed.emit()
+
     def from_mi(self, mi):
         val = mi.get(self.field, default='')
         self.current_val = val
@@ -486,7 +501,10 @@ class CompareSingle(QWidget):
     def revert(self, field):
         widgets = self.widgets[field]
         neww, oldw = widgets[:2]
-        neww.current_val = oldw.current_val
+        if hasattr(neww, 'set_undoable'):
+            neww.set_undoable(oldw.current_val)
+        else:
+            neww.current_val = oldw.current_val
 
     def merge_identifiers(self):
         widgets = self.widgets['identifiers']