הָעוֹבֵר לִפְנֵי הַתֵּיבָה, לֹא יַעֲנֶה אַחַר הַכֹּהֲנִים אָמֵן, מִפְּנֵי הַטֵּרוּף. וְאִם אֵין שָׁם כֹּהֵן אֶלָּא הוּא, לֹא יִשָּׂא אֶת כַּפָּיו. וְאִם הַבְטָחָתוֹ שֶׁהוּא נוֹשֵׂא אֶת כַּפָּיו וְחוֹזֵר לִתְפִלָּתוֹ, רַשַּׁאי:

One who leads the prayers should not respond after the blessing of the Kohanim "Amen", because of the lost concentration. If there is no Kohen there besides him (to recite the Priestly Blessing), he should not recite the Priestly Blessing (himself). But if he is confident that he will be able to recite the Priestly Blessing and return to his prayer, he is permitted.