diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 1557f5065e..35ef8c1f58 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -1967,7 +1967,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
 
     @classmethod
     def cleanup_tags(cls, tags):
-        tags = [x.strip() for x in tags if x.strip()]
+        tags = [x.strip().replace(',', ';') for x in tags if x.strip()]
         tags = [x.decode(preferred_encoding, 'replace') \
                     if isbytestring(x) else x for x in tags]
         tags = [u' '.join(x.split()) for x in tags]
diff --git a/src/calibre/library/schema_upgrades.py b/src/calibre/library/schema_upgrades.py
index 597cee8cfd..1483743e4a 100644
--- a/src/calibre/library/schema_upgrades.py
+++ b/src/calibre/library/schema_upgrades.py
@@ -427,7 +427,9 @@ class SchemaUpgrade(object):
 
     def upgrade_version_15(self):
         'Remove commas from tags'
-        self.conn.execute("UPDATE tags SET name=REPLACE(name, ',', ';')")
+        self.conn.execute("UPDATE OR IGNORE tags SET name=REPLACE(name, ',', ';')")
+        self.conn.execute("UPDATE OR IGNORE tags SET name=REPLACE(name, ',', ';;')")
+        self.conn.execute("UPDATE OR IGNORE tags SET name=REPLACE(name, ',', '')")
 
     def upgrade_version_16(self):
         self.conn.executescript('''