The solid-state structures of the synthetic psychedelic 5-meth-oxy-N,N-di-n-propyl-tryptamine (5-MeO-DPT) {systematic name: N-[2-(5-meth-oxy-1H-indol-3-yl)eth-yl]-N-propyl-propan-1-amine}, C17H25N2O, and its fumarate salt, bis-(5-meth-oxy-N,N-di-n-propyl-tryptammonium) fumarate (systematic name: bis-{N-[2-(5-meth-oxy-1H-indol-3-yl)eth-yl]-N-propyl-propan-1-aminium} but-2-ene-dio-ate), 2C17H25N2O+·C4H2O4 2-, are reported. The freebase has a single tryptamine mol-ecule in the asymmetric unit. The mol-ecules are linked together by N-H⋯N hydrogen bonds in zigzag chains along the [010] direction. The fumarate salt has a single tryptammonium cation and half of a fumarate dianion in the asymmetric unit. The tryptammonium and fumarate ions are held together in one-dimensional chains by a series of N-H⋯O hydrogen bonds. These chains are combinations of R 4 4(22) rings, and C 2 2(14) and C 4 4(28) parallel chains along [001].