Mac Miller drug supplier pleads guilty to fentanyl tax, 20-year max.

The man, as the prosecutors say, delivered the deadly pills that killed Mac Miller has admitted wrongdoing – to deal with a complaint agreement that could see him behind bars for a long time.

According to court documents obtained by TMZ, Stephen Walter pleaded guilty to federal charges in a single case of distribution of fentanyl. The second drug-related charge – conspiracy to distribute a controlled substance – was dropped.

Prosecutors alleged that Walter was the one who indirectly gave Mac’s alleged dealer, Cameron James Pettit, lethal Percocet tablets that ended up getting MM for FROM. As we reported, Pettit hit Walter … who then sent a runner to hand them over that fateful night.

As for what’s on the table for punishment … the doctors note that there is a maximum penalty he can risk – more than 20 years in prison – plus a life of supervised release and a $ 1 million fine. The prosecution recommends 17 years in prison and 5 years of supervised release.

There’s this too … prosecutors make a point by saying that Walter pleads guilty here means he was fully aware of what he pledged that night – counterfeit oxycodone pills filled with fentanyl.

And remember … Walter was ALREADY on monitored release from a previous drug case in which he was involved.