Simple jsp file (test.jsp): The referenced tagdir with one tagfile is trivial nonsense as well (attached). I can consistently reproduce the "CompositeLanguageFileViewProvider.updateOuterLanguageElements" exception (see attached stacktrace), by following the next steps: 1) Navigate to line 2 ("<%@ taglib prefix="foo" ...") 2) Duplicate (Ctrl-D). Now we're on line 3 3) On the new line 3, change "foo" into "c" 4) Still on line 3, select the following text: tagdir="/WEB-INF/tags/mytags" 5) Delete the selected text, but don't change caret position 6) Invoke completion (you should see "tagdir" and "uri" suggestions), but do not choose any suggestion yet After step 6, I get the mentioned error every time.