The disclosure relates to a scan chain circuit comprising cascaded flip-flops having a functional input node and a test input node configured to be selectively coupled to logic circuitry at a clock edge time. A clock line is provided configured to distribute one or more clock signals to the flip-flops in the chain, wherein the flip-flops in the chain have active clock edges applied thereto at respective clock edge times. The chain of flip-flops comprise a set of flip-flops configured to receive an edge inversion signal and to selectively invert their active clock edges in response to the edge inversion signal being asserted.