diff --git a/src/calibre/db/cache.py b/src/calibre/db/cache.py
index 30f0045c78..e3b02309f4 100644
--- a/src/calibre/db/cache.py
+++ b/src/calibre/db/cache.py
@@ -21,7 +21,7 @@ from queue import Queue
 from threading import Lock
 from time import sleep, time
 
-from calibre import as_unicode, isbytestring
+from calibre import as_unicode, isbytestring, detect_ncpus
 from calibre.constants import iswindows, preferred_encoding
 from calibre.customize.ui import (
     run_plugins_on_import, run_plugins_on_postadd, run_plugins_on_postimport
@@ -592,6 +592,15 @@ class Cache:
                 self.queue_next_fts_job()
         return existing
 
+    @api
+    def set_fts_speed(self, slow=True):
+        if slow:
+            self.fts_indexing_sleep_time = Cache.fts_indexing_sleep_time
+            self.set_fts_num_of_workers(1)
+        else:
+            self.fts_indexing_sleep_time = 0.1
+            self.set_fts_num_of_workers(max(1, detect_ncpus()))
+
     @read_api
     def fts_search(
         self,
diff --git a/src/calibre/gui2/fts/scan.py b/src/calibre/gui2/fts/scan.py
index 30f16ea721..c53a504376 100644
--- a/src/calibre/gui2/fts/scan.py
+++ b/src/calibre/gui2/fts/scan.py
@@ -8,8 +8,6 @@ from qt.core import (
     QRadioButton, QVBoxLayout, QWidget, pyqtSignal
 )
 
-from calibre import detect_ncpus
-from calibre.db.cache import Cache
 from calibre.db.listeners import EventType
 from calibre.db.utils import IndexingProgress
 from calibre.gui2.dialogs.confirm_delete import confirm
@@ -71,12 +69,7 @@ class ScanProgress(QWidget):
 
     def change_speed(self):
         db = get_db()
-        if self.fast_button.isChecked():
-            db.fts_indexing_sleep_time = 0.1
-            db.set_fts_num_of_workers(max(1, detect_ncpus()))
-        else:
-            db.fts_indexing_sleep_time = Cache.fts_indexing_sleep_time
-            db.set_fts_num_of_workers(1)
+        db.set_fts_speed(slow=not self.fast_button.isChecked())
         self.indexing_progress.clear_rate_information()
 
     def update(self, complete, left, total):