diff --git a/src/calibre/gui2/dialogs/metadata_bulk.py b/src/calibre/gui2/dialogs/metadata_bulk.py
index 3874f32b71..3aac439815 100644
--- a/src/calibre/gui2/dialogs/metadata_bulk.py
+++ b/src/calibre/gui2/dialogs/metadata_bulk.py
@@ -712,7 +712,8 @@ class MetadataBulkDialog(ResizableDialog, Ui_MetadataBulkDialog):
         dest_mode = self.replace_mode.currentIndex()
 
         if self.destination_field_fm['is_csp']:
-            if not unicode(self.s_r_dst_ident.text()):
+            dest_ident = unicode(self.s_r_dst_ident.text())
+            if not dest_ident or (src == 'identifiers' and dest_ident == '*'):
                 raise Exception(_('You must specify a destination identifier type'))
 
         if self.destination_field_fm['is_multiple']:
@@ -816,13 +817,18 @@ class MetadataBulkDialog(ResizableDialog, Ui_MetadataBulkDialog):
                 # convert the colon-separated pair strings back into a dict,
                 # which is what set_identifiers wants
                 dst_id_type = unicode(self.s_r_dst_ident.text())
-                if dst_id_type:
+                if dst_id_type and dst_id_type != '*':
                     v = ''.join(val)
                     ids = mi.get(dest)
                     ids[dst_id_type] = v
                     val = ids
                 else:
-                    val = dict([(t.split(':')) for t in val])
+                    try:
+                        val = dict([(t.split(':')) for t in val])
+                    except:
+                        raise Exception(_('Invalid identifier string. It must be a '
+                                          'comma-separated list of pairs of '
+                                          'strings separated by a colon'))
         else:
             val = self.s_r_replace_mode_separator().join(val)
             if dest == 'title' and len(val) == 0:
diff --git a/src/calibre/gui2/dialogs/metadata_bulk.ui b/src/calibre/gui2/dialogs/metadata_bulk.ui
index 24a84eb1b4..6387626e58 100644
--- a/src/calibre/gui2/dialogs/metadata_bulk.ui
+++ b/src/calibre/gui2/dialogs/metadata_bulk.ui
@@ -504,7 +504,7 @@ from the value in the box</string>
              <item>
               <widget class="QCheckBox" name="restore_original">
                <property name="toolTip">
-                <string>When doing a same format to same format conversion, 
+                <string>When doing a same format to same format conversion,
 for e.g., EPUB to EPUB, calibre saves the original EPUB
  as ORIGINAL_EPUB. This option tells calibre to restore
  the EPUB from ORIGINAL_EPUB. Useful if you did a bulk
@@ -1006,7 +1006,10 @@ not multiple and the destination field is multiple</string>
               </sizepolicy>
              </property>
              <property name="toolTip">
-              <string>Choose which identifier type to operate upon</string>
+              <string>&lt;p&gt;Choose which identifier type to operate upon. If the
+              source field is something other than 'identifiers' you can enter
+              a * if you want to replace the entire set of identifiers with
+              the result of the search/replace.&lt;/p&gt;</string>
              </property>
             </widget>
            </item>