This paper presents results from a computational and laboratory investigation of wind flow and fire spread over an isolated sloped-ridgeline laboratory-scale hill under various slopes with the wind blowing perpendicularly to the ridgeline. The results show two situations of unexpected or unusual fire behaviour; one is a lateral spread of the fire front over the windward face into a down-ridge direction resulting from a strong near-surface flow component parallel to the ridgeline. The other behaviour is a lateral enlargement of the fire front near the ridgeline over the leeward face in an up-ridge direction resulting from a flow parallel to the ridgeline. Comparison with reference fire spread rates and wind flow observations highlight the importance of the interaction between terrain-modified flow mechanisms and the fire in which they result in accelerated flows that drive the indicated unexpected behaviour.