The invention provides crystalline solid forms of (S)-4-((2S,3S)-7-carbamoyl-1,1-diethyl-3-methoxy-1,2,3,4-tetrahydronaphthalen-2-ylamino)-2-cyclohexylmethyl-butyric acid. The invention also provides pharmaceutical compositions comprising such crystalline solid forms, methods of using such crystalline solid forms to treat diseases associated with mu opioid receptor activity, and processes useful for preparing such crystalline solid forms.