Be certain to proofread your manuscript thoroughly.  Don't simply run a spell check program and think that is good enough--in this case, the spell check and even a grammar check does not reveal the error.  Such errors take away greatly from the quality of a manuscript as they leave the reader with the sense that the utmost care was not taken with the product.  Have a friend read over the manuscript or put it down and come back to it yourself at a later time.  Also, if you are very concerned, read you paper backwards to force you to concentrate on the spelling of words since the syntax is completely eradicated.