Clapeyron equation: dp/dT = ΔS / ΔV

Question

My textbook says, for fusion/melting reactions: dp/dT = ΔH / (T ΔV)

this implies that T * ΔS = ΔH.

I know T * ΔS = q and at constant pressure, that equals H, but the dp/dT reaction is not at constant pressure. Please explain. Thanks!