פירוש על קידושין 101:9

Rava explained that since one cannot marry a woman and then her sister, if one marries two sisters at the same time, neither are married. This follows Rabbah’s principle. But Rava could have invoked a different principle, one that he uses elsewhere. Kiddushin which create a situation in which the couple may not have sex do not count as kiddushin. This is the situation here. If the man was married to both sisters, he could not have sex with either because each is his wife’s sister.
The Talmud explains that Rava was explaining it according to the verse used by Rami b. Hama to explain the mishnah (see end of daf Nun). Rava said that the verse Rami b. Hama used cannot explain the mishnah because it refers to a man who marries a woman and then her sister, whereas the mishnah refers to a man who marries both at the same time.