diff --git a/src/calibre/gui2/comments_editor.py b/src/calibre/gui2/comments_editor.py
index 50de42a3be..dbef2c5707 100644
--- a/src/calibre/gui2/comments_editor.py
+++ b/src/calibre/gui2/comments_editor.py
@@ -13,7 +13,7 @@ from PyQt5.Qt import (QApplication, QFontInfo, QSize, QWidget, QPlainTextEdit,
     QToolBar, QVBoxLayout, QAction, QIcon, Qt, QTabWidget, QUrl, QFormLayout,
     QSyntaxHighlighter, QColor, QColorDialog, QMenu, QDialog, QLabel,
     QHBoxLayout, QKeySequence, QLineEdit, QDialogButtonBox, QPushButton,
-    QCheckBox)
+    pyqtSignal, QCheckBox)
 from PyQt5.QtWebKitWidgets import QWebView, QWebPage
 try:
     from PyQt5 import sip
@@ -74,6 +74,8 @@ class BlockStyleAction(QAction):  # {{{
 
 class EditorWidget(QWebView, LineEditECM):  # {{{
 
+    data_changed = pyqtSignal()
+
     def __init__(self, parent=None):
         QWebView.__init__(self, parent)
         self.base_url = None
@@ -184,6 +186,7 @@ class EditorWidget(QWebView, LineEditECM):  # {{{
 
         self.setHtml('')
         self.set_readonly(False)
+        self.page().contentsChanged.connect(self.data_changed)
 
     def update_link_action(self):
         wac = self.pageAction(QWebPage.ToggleBold).isEnabled()
@@ -660,6 +663,7 @@ class Highlighter(QSyntaxHighlighter):
 class Editor(QWidget):  # {{{
 
     toolbar_prefs_name = None
+    data_changed = pyqtSignal()
 
     def __init__(self, parent=None, one_line_toolbar=False, toolbar_prefs_name=None):
         QWidget.__init__(self, parent)
@@ -671,6 +675,7 @@ class Editor(QWidget):  # {{{
             t = getattr(self, 'toolbar%d'%i)
             t.setIconSize(QSize(18, 18))
         self.editor = EditorWidget(self)
+        self.editor.data_changed.connect(self.data_changed)
         self.set_base_url = self.editor.set_base_url
         self.set_html = self.editor.set_html
         self.tabs = QTabWidget(self)
diff --git a/src/calibre/gui2/custom_column_widgets.py b/src/calibre/gui2/custom_column_widgets.py
index 5d226605e0..6be662bc81 100644
--- a/src/calibre/gui2/custom_column_widgets.py
+++ b/src/calibre/gui2/custom_column_widgets.py
@@ -25,12 +25,20 @@ from calibre.gui2.library.delegates import ClearingDoubleSpinBox, ClearingSpinBo
 from calibre.gui2.widgets2 import RatingEditor
 
 
+def safe_disconnect(signal):
+    try:
+        signal.disconnect()
+    except Exception:
+        pass
+
+
 class Base(object):
 
     def __init__(self, db, col_id, parent=None):
         self.db, self.col_id = db, col_id
         self.col_metadata = db.custom_column_num_map[col_id]
         self.initial_val = self.widgets = None
+        self.signals_to_disconnect = []
         self.setup_ui(parent)
 
     def initialize(self, book_id):
@@ -66,6 +74,12 @@ class Base(object):
 
     def break_cycles(self):
         self.db = self.widgets = self.initial_val = None
+        for signal in self.signals_to_disconnect:
+            safe_disconnect(signal)
+        self.signals_to_disconnect = []
+
+    def connect_data_changed(self, slot):
+        pass
 
 
 class SimpleText(Base):
@@ -79,6 +93,10 @@ class SimpleText(Base):
     def getter(self):
         return self.widgets[1].text().strip()
 
+    def connect_data_changed(self, slot):
+        self.widgets[1].textChanged.connect(slot)
+        self.signals_to_disconnect.append(self.widgets[1].textChanged)
+
 
 class LongText(Base):
 
@@ -98,6 +116,10 @@ class LongText(Base):
     def getter(self):
         return self._tb.toPlainText()
 
+    def connect_data_changed(self, slot):
+        self._tb.textChanged.connect(slot)
+        self.signals_to_disconnect.append(self._tb.textChanged)
+
 
 class Bool(Base):
 
@@ -165,6 +187,10 @@ class Bool(Base):
     def set_to_cleared(self):
         self.combobox.setCurrentIndex(2)
 
+    def connect_data_changed(self, slot):
+        self.combobox.currentTextChanged.connect(slot)
+        self.signals_to_disconnect.append(self.combobox.currentTextChanged)
+
 
 class Int(Base):
 
@@ -195,6 +221,10 @@ class Int(Base):
             self.setter(0)
         self.was_none = to_what == self.widgets[1].minimum()
 
+    def connect_data_changed(self, slot):
+        self.widgets[1].valueChanged.connect(slot)
+        self.signals_to_disconnect.append(self.widgets[1].valueChanged)
+
 
 class Float(Int):
 
@@ -223,6 +253,10 @@ class Rating(Base):
     def getter(self):
         return self.widgets[1].rating_value or None
 
+    def connect_data_changed(self, slot):
+        self.widgets[1].currentTextChanged.connect(slot)
+        self.signals_to_disconnect.append(self.widgets[1].currentTextChanged)
+
 
 class DateTimeEdit(QDateTimeEdit):
 
@@ -302,6 +336,10 @@ class DateTime(Base):
     def normalize_ui_val(self, val):
         return as_utc(val) if val is not None else None
 
+    def connect_data_changed(self, slot):
+        self.widgets[1].dateTimeChanged.connect(slot)
+        self.signals_to_disconnect.append(self.widgets[1].dateTimeChanged)
+
 
 class Comments(Base):
 
@@ -345,6 +383,10 @@ class Comments(Base):
             self._tb.tab = val
         return property(fget=fget, fset=fset)
 
+    def connect_data_changed(self, slot):
+        self._tb.data_changed.connect(slot)
+        self.signals_to_disconnect.append(self._tb.data_changed)
+
 
 class MultipleWidget(QWidget):
 
@@ -481,6 +523,14 @@ class Text(Base):
         if d.exec_() == TagEditor.Accepted:
             self.setter(d.tags)
 
+    def connect_data_changed(self, slot):
+        if self.col_metadata['is_multiple']:
+            s = self.widgets[1].tags_box.currentTextChanged
+        else:
+            s = self.widgets[1].currentTextChanged
+        s.connect(slot)
+        self.signals_to_disconnect.append(s)
+
 
 class Series(Base):
 
@@ -554,6 +604,11 @@ class Series(Base):
         val, s_index = self.current_val
         mi.set('#' + self.col_metadata['label'], val, extra=s_index)
 
+    def connect_data_changed(self, slot):
+        for s in self.widgets[1].editTextChanged, self.widgets[3].valueChanged:
+            s.connect(slot)
+            self.signals_to_disconnect.append(s)
+
 
 class Enumeration(Base):
 
@@ -598,6 +653,10 @@ class Enumeration(Base):
             val = None
         return val
 
+    def connect_data_changed(self, slot):
+        self.widgets[1].currentIndexChanged.connect(slot)
+        self.signals_to_disconnect.append(self.widgets[1].currentIndexChanged)
+
 
 def comments_factory(db, key, parent):
     fm = db.custom_column_num_map[key]
diff --git a/src/calibre/gui2/metadata/basic_widgets.py b/src/calibre/gui2/metadata/basic_widgets.py
index 930435c4fd..bdd5380633 100644
--- a/src/calibre/gui2/metadata/basic_widgets.py
+++ b/src/calibre/gui2/metadata/basic_widgets.py
@@ -195,12 +195,14 @@ class TitleEdit(EnLineEdit, ToMetadataMixin):
     TITLE_ATTR = FIELD_NAME = 'title'
     TOOLTIP = _('Change the title of this book')
     LABEL = _('&Title:')
+    data_changed = pyqtSignal()
 
     def __init__(self, parent):
         self.dialog = parent
         EnLineEdit.__init__(self, parent)
         self.setToolTip(self.TOOLTIP)
         self.setWhatsThis(self.TOOLTIP)
+        self.textChanged.connect(self.data_changed)
 
     def get_default(self):
         return _('Unknown')
@@ -331,6 +333,7 @@ class AuthorsEdit(EditWithComplete, ToMetadataMixin):
     TOOLTIP = ''
     LABEL = _('&Author(s):')
     FIELD_NAME = 'authors'
+    data_changed = pyqtSignal()
 
     def __init__(self, parent, manage_authors):
         self.dialog = parent
@@ -343,6 +346,7 @@ class AuthorsEdit(EditWithComplete, ToMetadataMixin):
         self.manage_authors_signal = manage_authors
         manage_authors.triggered.connect(self.manage_authors)
         self.lineEdit().createStandardContextMenu = self.createStandardContextMenu
+        self.lineEdit().textChanged.connect(self.data_changed)
 
     def createStandardContextMenu(self):
         menu = QLineEdit.createStandardContextMenu(self.lineEdit())
@@ -444,6 +448,7 @@ class AuthorSortEdit(EnLineEdit, ToMetadataMixin):
             'red, then the authors and this text do not match.')
     LABEL = _('Author s&ort:')
     FIELD_NAME = 'author_sort'
+    data_changed = pyqtSignal()
 
     def __init__(self, parent, authors_edit, autogen_button, db,
             copy_a_to_as_action, copy_as_to_a_action, a_to_as, as_to_a):
@@ -463,6 +468,7 @@ class AuthorSortEdit(EnLineEdit, ToMetadataMixin):
 
         self.authors_edit.editTextChanged.connect(self.update_state_and_val, type=Qt.QueuedConnection)
         self.textChanged.connect(self.update_state)
+        self.textChanged.connect(self.data_changed)
 
         self.autogen_button = autogen_button
         self.copy_a_to_as_action = copy_a_to_as_action
@@ -591,6 +597,7 @@ class SeriesEdit(EditWithComplete, ToMetadataMixin):
     TOOLTIP = _('List of known series. You can add new series.')
     LABEL = _('&Series:')
     FIELD_NAME = 'series'
+    data_changed = pyqtSignal()
 
     def __init__(self, parent):
         EditWithComplete.__init__(self, parent)
@@ -602,6 +609,7 @@ class SeriesEdit(EditWithComplete, ToMetadataMixin):
         self.setWhatsThis(self.TOOLTIP)
         self.setEditable(True)
         self.books_to_refresh = set([])
+        self.lineEdit().textChanged.connect(self.data_changed)
 
     @dynamic_property
     def current_val(self):
@@ -645,9 +653,11 @@ class SeriesIndexEdit(make_undoable(QDoubleSpinBox), ToMetadataMixin):
     TOOLTIP = ''
     LABEL = _('&Number:')
     FIELD_NAME = 'series_index'
+    data_changed = pyqtSignal()
 
     def __init__(self, parent, series_edit):
         super(SeriesIndexEdit, self).__init__(parent)
+        self.valueChanged.connect(self.data_changed)
         self.dialog = parent
         self.db = self.original_series_name = None
         self.setMaximum(10000000)
@@ -795,11 +805,23 @@ class FormatList(_FormatList):
 
 class FormatsManager(QWidget):
 
+    data_changed = pyqtSignal()
+
+    @property
+    def changed(self):
+        return self._changed
+
+    @changed.setter
+    def changed(self, val):
+        self._changed = val
+        if val:
+            self.data_changed.emit()
+
     def __init__(self, parent, copy_fmt):
         QWidget.__init__(self, parent)
         self.dialog = parent
         self.copy_fmt = copy_fmt
-        self.changed = False
+        self._changed = False
 
         self.l = l = QGridLayout()
         self.setLayout(l)
@@ -1031,6 +1053,7 @@ class FormatsManager(QWidget):
 class Cover(ImageView):  # {{{
 
     download_cover = pyqtSignal()
+    data_changed = pyqtSignal()
 
     def __init__(self, parent):
         ImageView.__init__(self, parent, show_size_pref_name='edit_metadata_cover_widget', default_show_size=True)
@@ -1202,6 +1225,7 @@ class Cover(ImageView):  # {{{
                 tt = _('Cover size: %(width)d x %(height)d pixels') % \
                 dict(width=pm.width(), height=pm.height())
             self.setToolTip(tt)
+            self.data_changed.emit()
 
         return property(fget=fget, fset=fset)
 
@@ -1245,6 +1269,7 @@ class CommentsEdit(Editor, ToMetadataMixin):  # {{{
                 val = comments_to_html(val)
             self.set_html(val, self.allow_undo)
             self.wyswyg_dirtied()
+            self.data_changed.emit()
         return property(fget=fget, fset=fset)
 
     def initialize(self, db, id_):
@@ -1265,11 +1290,13 @@ class RatingEdit(RatingEditor, ToMetadataMixin):  # {{{
     LABEL = _('&Rating:')
     TOOLTIP = _('Rating of this book. 0-5 stars')
     FIELD_NAME = 'rating'
+    data_changed = pyqtSignal()
 
     def __init__(self, parent):
         super(RatingEdit, self).__init__(parent)
         self.setToolTip(self.TOOLTIP)
         self.setWhatsThis(self.TOOLTIP)
+        self.currentTextChanged.connect(self.data_changed)
 
     @dynamic_property
     def current_val(self):
@@ -1301,9 +1328,11 @@ class TagsEdit(EditWithComplete, ToMetadataMixin):  # {{{
             'useful while searching. <br><br>They can be any words '
             'or phrases, separated by commas.')
     FIELD_NAME = 'tags'
+    data_changed = pyqtSignal()
 
     def __init__(self, parent):
         EditWithComplete.__init__(self, parent)
+        self.currentTextChanged.connect(self.data_changed)
         self.lineEdit().setMaxLength(655360)  # see https://bugs.launchpad.net/bugs/1630944
         self.books_to_refresh = set([])
         self.setToolTip(self.TOOLTIP)
@@ -1366,9 +1395,11 @@ class LanguagesEdit(LE, ToMetadataMixin):  # {{{
     LABEL = _('&Languages:')
     TOOLTIP = _('A comma separated list of languages for this book')
     FIELD_NAME = 'languages'
+    data_changed = pyqtSignal()
 
     def __init__(self, *args, **kwargs):
         LE.__init__(self, *args, **kwargs)
+        self.textChanged.connect(self.data_changed)
         self.setToolTip(self.TOOLTIP)
 
     @dynamic_property
@@ -1458,11 +1489,13 @@ class IdentifiersEdit(QLineEdit, ToMetadataMixin):
             'For example: \n\n%s\n\nIf an identifier value contains a comma, you can use the | character to represent it.')%(
             'isbn:1565927249, doi:10.1000/182, amazon:1565927249')
     FIELD_NAME = 'identifiers'
+    data_changed = pyqtSignal()
 
     def __init__(self, parent):
         QLineEdit.__init__(self, parent)
         self.pat = re.compile(r'[^0-9a-zA-Z]')
         self.textChanged.connect(self.validate)
+        self.textChanged.connect(self.data_changed)
 
     def contextMenuEvent(self, ev):
         m = self.createStandardContextMenu()
@@ -1631,9 +1664,11 @@ class ISBNDialog(QDialog):  # {{{
 class PublisherEdit(EditWithComplete, ToMetadataMixin):  # {{{
     LABEL = _('&Publisher:')
     FIELD_NAME = 'publisher'
+    data_changed = pyqtSignal()
 
     def __init__(self, parent):
         EditWithComplete.__init__(self, parent)
+        self.currentTextChanged.connect(self.data_changed)
         self.set_separator(None)
         self.setSizeAdjustPolicy(
                 self.AdjustToMinimumContentsLengthWithIcon)
@@ -1694,11 +1729,13 @@ class DateEdit(make_undoable(QDateTimeEdit), ToMetadataMixin):
     FMT = 'dd MMM yyyy hh:mm:ss'
     ATTR = FIELD_NAME = 'timestamp'
     TWEAK = 'gui_timestamp_display_format'
+    data_changed = pyqtSignal()
 
     def __init__(self, parent, create_clear_button=True):
         super(DateEdit, self).__init__(parent)
         self.setToolTip(self.TOOLTIP)
         self.setWhatsThis(self.TOOLTIP)
+        self.dateTimeChanged.connect(self.data_changed)
         fmt = tweaks[self.TWEAK]
         if fmt is None:
             fmt = self.FMT
diff --git a/src/calibre/gui2/metadata/single.py b/src/calibre/gui2/metadata/single.py
index 037a032a4c..6020a671e5 100644
--- a/src/calibre/gui2/metadata/single.py
+++ b/src/calibre/gui2/metadata/single.py
@@ -17,6 +17,7 @@ from PyQt5.Qt import (Qt, QVBoxLayout, QHBoxLayout, QWidget, QPushButton,
         QSizePolicy, QFrame, QSize, QKeySequence, QMenu, QShortcut, QDialog)
 
 from calibre.constants import isosx
+from calibre.gui2.dialogs.confirm_delete import confirm
 from calibre.ebooks.metadata import authors_to_string, string_to_authors
 from calibre.gui2 import error_dialog, gprefs, pixmap_to_data
 from calibre.gui2.metadata.basic_widgets import (TitleEdit, AuthorsEdit,
@@ -56,6 +57,7 @@ class MetadataSingleDialogBase(QDialog):
 
     def __init__(self, db, parent=None, editing_multiple=False):
         self.db = db
+        self.was_data_edited = False
         self.changed = set()
         self.books_to_refresh = set()
         self.rows_to_refresh = set()
@@ -292,6 +294,8 @@ class MetadataSingleDialogBase(QDialog):
         self.config_metadata_button.clicked.connect(self.configure_metadata)
         self.config_metadata_button.setToolTip(
             _('Change how calibre downloads metadata'))
+        for w in self.basic_metadata_widgets:
+            w.data_changed.connect(self.data_changed)
 
     # }}}
 
@@ -320,6 +324,7 @@ class MetadataSingleDialogBase(QDialog):
                 two_column=self.cc_two_column)
         self.__custom_col_layouts = [layout]
         for widget in self.custom_metadata_widgets:
+            widget.connect_data_changed(self.data_changed)
             if isinstance(widget, Comments):
                 self.comments_edit_state_at_apply[widget] = None
     # }}}
@@ -353,6 +358,9 @@ class MetadataSingleDialogBase(QDialog):
     def do_layout(self):
         raise NotImplementedError()
 
+    def data_changed(self):
+        self.was_data_edited = True
+
     def __call__(self, id_):
         self.book_id = id_
         self.books_to_refresh = set([])
@@ -363,6 +371,7 @@ class MetadataSingleDialogBase(QDialog):
             widget.initialize(id_)
         if callable(self.set_current_callback):
             self.set_current_callback(id_)
+        self.was_data_edited = False
         # Commented out as it doesn't play nice with Next, Prev buttons
         # self.fetch_metadata_button.setFocus(Qt.OtherFocusReason)
 
@@ -620,6 +629,10 @@ class MetadataSingleDialogBase(QDialog):
 
     def reject(self):
         self.save_state()
+        if self.was_data_edited and not confirm(
+                title=_('Are you sure?'), name='confirm-cancel-edit-single-metadata', msg=_(
+                    'You will lose all unsaved changes, are you sure?'), parent=self):
+            return
         QDialog.reject(self)
 
     def save_state(self):