diff --git a/src/testdir/test_blob.vim b/src/testdir/test_blob.vim
index 2e5ef0b..0170f54 100644
--- a/src/testdir/test_blob.vim
+++ b/src/testdir/test_blob.vim
@@ -257,6 +257,9 @@
   let br = readfile('Xblob', 'B')
   call assert_equal(b, br)
   call delete('Xblob')
+
+  " This was crashing when calling readfile() with a directory.
+  call assert_fails("call readfile('.', 'B')", 'E17: "." is a directory')
 endfunc
 
 " filter() item in blob