diff --git a/anki/features/japanese.py b/anki/features/japanese.py
index cb0e3f4e0..e9ee3f4e6 100644
--- a/anki/features/japanese.py
+++ b/anki/features/japanese.py
@@ -99,6 +99,8 @@ def onFocusLost(fact, field):
             return
     except:
         return
-    fact['Reading'] = kakasi.toFurigana(field.value)
+    tmp = kakasi.toFurigana(field.value)
+    if tmp != field.value:
+        fact['Reading'] = tmp
 
 addHook('fact.focusLost', onFocusLost)