diff --git a/tests/test-largefiles.t b/tests/test-largefiles.t
--- a/tests/test-largefiles.t
+++ b/tests/test-largefiles.t
@@ -1128,7 +1128,8 @@ largefiles clients refuse to push largef
   $ cd ..
 
 putlfile errors are shown (issue3123)
-Corrupt the cached largefile in r7
+Corrupt the cached largefile in r7 and in the usercache (required for testing on vfat)
+  $ echo corruption > "$TESTTMP/r7/.hg/largefiles/4cdac4d8b084d0b599525cf732437fb337d422a8"
   $ echo corruption > "$USERCACHE/4cdac4d8b084d0b599525cf732437fb337d422a8"
   $ hg init empty
   $ hg serve -R empty -d -p $HGPORT1 --pid-file hg.pid \