Story highlights The quote appears on a new "forever" postage stamp

Another author confirms that it is hers

"The sentence held great meaning for her," Postage Service says

(CNN) The late author/poet Maya Angelou was well-known for her many thought-provoking quotes, but it appears that one that was used for her stamp is not actually hers.

The Washington Post reports that a new United States postage stamp bearing Angelou's likeness features the quote "A bird doesn't sing because it has an answer, it sings because it has a song." Problem is, that's a quote from a book of poems by Joan Walsh Anglund.

"Yes, that's my quote," Anglund told the Post on Monday.

The paper reports that the quote appears in Anglund's 1967 book "A Cup of Sun." The pronouns and punctuation were changed, with "he" in the original verse changed to "it" on the stamp.

A spokesman for the Postal Service defended the use of the quote on the "forever" stamp, saying it had been widely attributed to Angelou.