diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index b10f96d..57115de 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
@@ -1212,7 +1212,9 @@
   call DiffMaintainsChangeMark()
   set diffopt+=internal
   call DiffMaintainsChangeMark()
+
   set diffopt&
+  delfunc DiffMaintainsChangeMark
 endfunc
 
 " Test for 'patchexpr'