diff --git a/src/testdir/test_largefile.vim b/src/testdir/test_largefile.vim
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+" Tests for large files
+" This is only executed manually: "make test_largefile".
+" This is not run as part of "make test".
+
+func Test_largefile()
+  let fname = 'Xlarge.txt'
+
+  call delete(fname)
+  exe "e" fname
+  " Make sure that a line break is 1 byte (LF).
+  set ff=unix
+  set undolevels=-1
+  " Input 99 'A's. The line becomes 100 bytes including a line break.
+  exe "normal 99iA\<Esc>"
+  yank
+  " Put 39,999,999 times. The file becomes 4,000,000,000 bytes.
+  normal 39999999p
+  " Moving around in the file randomly.
+  normal G
+  normal 10%
+  normal 90%
+  normal 50%
+  normal gg
+  w
+  " Check if the file size is larger than 2^31 - 1 bytes.
+  " Note that getfsize() returns -2 if a Number is 32 bits.
+  let fsize=getfsize(fname)
+  call assert_true(fsize > 2147483647 || fsize == -2)
+  "call delete(fname)
+endfunc