This document discloses a solution for preamble detection. According to an aspect, a method comprises: transmitting a message to a first terminal device connected to an access node, the message instructing the terminal device to carry out a random access procedure towards the access node; receiving a signal from the first terminal device during the random access procedure, the signal comprising a random access preamble; using the received signal as a training input in a random access preamble detection process; and using the random access preamble detection process trained with the training input in detection of a random access preamble from a second terminal device not connected to the access node.