When a sentence contains repeated words, most spell-checking programs will highlight the extra word. It’s a fairly common form of typo. But there are also times when a sentence has been deliberately constructed with double words:

I assured them that that wouldn’t happen.

The spell-checker flags this as a mistake but is it incorrect?

Another example: They were instructed to give her her job back.

Both of our examples are grammatically correct, but some may find them a bit awkward. A simple rewrite can often eliminate the problem.

I assured them that it wouldn’t happen.
They were instructed to reinstate her job.

One other source of confusion is the construction of “had.”

They had had some trouble with their neighbors long before this lawsuit.
If I had had an extra pencil, I would have finished the exam in time.

These are examples of the correct usage of the past perfect form of “have” when it refers back to an earlier past time.

A more troublesome usage of double words involves “is,” as in, The trouble is is that you are from out of town. Or The fact is is that the weather won’t cooperate.

This is incorrect, as well as awkward, and should be rewritten. The trouble is that you are from out of town. The subjects of the sentences are “the trouble” and “the fact,” which require only one verb—“is.”

Sometimes writers try to fix the problem by adding a comma. The question is, is the man going to stick around? The general construction of these “the problem is, the question is” sentences is inherently ungainly and should probably be avoided.

So, do not be unnecessarily troubled by doubled words. If you are unhappy with them, reword your sentence.

As soon as I wrote it, it started to make sense.