Poison rule clarification

Hi I had a quick question about how the Poison rule worked.

Lets say a Grotesque is attacking a Toughness 3 model. His Strength 5 would have him wounding on 2's, but the weapon is poison (4+). So to re-roll poisoned attacks do you have to roll wounding on 4's, or do you still re-roll wounding on 2's?

You wound on 2+, re-rolling any failed rolls.