diff --git a/resources/default_tweaks.py b/resources/default_tweaks.py
index b4ce1f1589..92323d0f0f 100644
--- a/resources/default_tweaks.py
+++ b/resources/default_tweaks.py
@@ -506,3 +506,17 @@ change_book_details_font_size_by = 0
 # No compile: compile_gpm_templates = False
 compile_gpm_templates = True
 
+#: What format to default to when using the Tweak feature
+# The Tweak feature of calibre allows direct editing of a book format.
+# If multiple formats are available, calibre will offer you a choice
+# of formats, defaulting to your preferred output format if it is available.
+# Set this tweak to a specific value of 'EPUB' or 'AZW3' to always default
+# to that format rather than your output format preference.
+# Set to a value of 'remember' to use whichever format you chose last time you
+# used the Tweak feature.
+# Examples:
+#   default_tweak_format = None       (Use output format)
+#   default_tweak_format = 'EPUB'
+#   default_tweak_format = 'remember'
+default_tweak_format = None
+
diff --git a/src/calibre/gui2/actions/tweak_epub.py b/src/calibre/gui2/actions/tweak_epub.py
index 0d5f8ec8f5..0872849c8c 100755
--- a/src/calibre/gui2/actions/tweak_epub.py
+++ b/src/calibre/gui2/actions/tweak_epub.py
@@ -12,11 +12,11 @@ from PyQt4.Qt import (QDialog, QVBoxLayout, QHBoxLayout, QRadioButton, QFrame,
 
 from calibre import as_unicode
 from calibre.constants import isosx
-from calibre.gui2 import error_dialog, question_dialog, open_local_file
+from calibre.gui2 import error_dialog, question_dialog, open_local_file, gprefs
 from calibre.gui2.actions import InterfaceAction
 from calibre.ptempfile import (PersistentTemporaryDirectory,
         PersistentTemporaryFile)
-from calibre.utils.config import prefs
+from calibre.utils.config import prefs, tweaks
 
 class TweakBook(QDialog):
 
@@ -32,11 +32,16 @@ class TweakBook(QDialog):
             index_is_id=True))
 
         button = self.fmt_choice_buttons[0]
+        button_map = {unicode(x.text()):x for x in self.fmt_choice_buttons}
         of = prefs['output_format'].upper()
-        for x in self.fmt_choice_buttons:
-            if unicode(x.text()) == of:
-                button = x
-                break
+        df = tweaks.get('default_tweak_format', None)
+        lf = gprefs.get('last_tweak_format', None)
+        if df and df.lower() == 'remember' and lf in button_map:
+            button = button_map[lf]
+        elif df and df.upper() in button_map:
+            button = button_map[df.upper()]
+        elif of in button_map:
+            button = button_map[of]
         button.setChecked(True)
 
         self.init_state()
@@ -148,6 +153,8 @@ class TweakBook(QDialog):
 
     def explode(self):
         self.show_msg(_('Exploding, please wait...'))
+        if len(self.fmt_choice_buttons) > 1:
+            gprefs.set('last_tweak_format', self.current_format.upper())
         QTimer.singleShot(5, self.do_explode)
 
     def ask_question(self, msg):