In forensic entomology, the determination of a minimum post-mortem interval often relies on the determination of the age of blow flies, since they are generally among the first colonisers of a corpse. In indoor cases, the blow flies might be delayed in arriving at the corpse. If the windows are closed, the attracting odour is confined and does not reach the flies, so that it takes longer for them to find and access the corpse. If blow flies are delayed or are unable to reach a corpse lying inside a room, much smaller flies (Phoridae) can enter and deposit their offspring. We present three indoor-case scenarios in which age determination of Megaselia scalaris gave much more accurate estimates of the minimum post-mortem interval than from larvae of Calliphoridae. In all cases, the estimated age of the blow fly larvae was between 10 and 20 days too short compared to the actual PMI. Estimation of the PMI using developmental times of Phoridae can be a good alternative to the determination of blow fly larval age, since Phoridae are found inside apparently enclosed environments (sealed plastic bags or rooms with closed doors and windows) and also at temperatures at which blow flies are inactive.