diff --git a/src/calibre/gui2/actions/edit_metadata.py b/src/calibre/gui2/actions/edit_metadata.py
index daa9cef01b..650947100e 100644
--- a/src/calibre/gui2/actions/edit_metadata.py
+++ b/src/calibre/gui2/actions/edit_metadata.py
@@ -488,8 +488,8 @@ class EditMetadataAction(InterfaceAction):
             if self._am_merge_tags:
                 old_tags = db.tags(i, index_is_id=True)
                 if old_tags:
-                    tags = old_tags.split(',') + (mi.tags if mi.tags else
-                            [])
+                    tags = [x.strip() for x in old_tags.split(',')] + (
+                            mi.tags if mi.tags else [])
                     mi.tags = list(set(tags))
             db.set_metadata(i, mi, commit=False, set_title=set_title,
                     set_authors=set_authors, notify=False)