In 1991 Professor Xi Ougen put forward the proposition that
the homomorphic image of a fuzzy ideal with sup property 
of a BCK-algebra is also a fuzzy ideal.(cf. Proposition 5 of [1].) 
It is pointed out that there is a mistake in its proof presented in [1], 
although the proposition itself is correct. 
In this paper the proposition is generalized to BCH-algebras
and a new correct proof is given. 
Moreover, the condition of sup property is removed.