diff -r 17ba2df56dee -r ade12ef2773c src/HOL/Library/Bit.thy
--- a/src/HOL/Library/Bit.thy	Mon Jul 06 22:06:02 2015 +0200
+++ b/src/HOL/Library/Bit.thy	Mon Jul 06 22:57:34 2015 +0200
@@ -123,8 +123,8 @@
   plus_bit_def times_bit_def minus_bit_def uminus_bit_def
   divide_bit_def inverse_bit_def
 
-instance proof
-qed (unfold field_bit_defs, auto split: bit.split)
+instance
+  by standard (auto simp: field_bit_defs split: bit.split)
 
 end