A hydraulic rotary-percussive hammer drill including: - a hammer drill body, - a fluid injection portion provided on a front portion of the hammer drill body, the fluid injection portion comprising a longitudinal passage, a fluid feed-in inlet intended to be fluidly connected to an injection fluid source and an annular inner groove fluidly connected to the fluid feed-in inlet and opening into the longitudinal passage, - a shank intended to be coupled to at least one drill bar equipped with a tool, the shank having a longitudinal axis and extending in the longitudinal passage of the fluid injection portion, the annular inner groove extending around the shank, the shank including a fluid injection conduit extending over at least a portion of the length of the shank and a communication orifice configured to fluidly connect the annular inner groove and the fluid injection conduit, - a striking piston slidably mounted inside the hammer drill body along a striking axis and configured to hit the shank, - a front main sealing gasket and a rear main sealing gasket which are annular and each extending around the shank, the front and rear main sealing gaskets (26, 27) being fastened to the fluid injection portion and being disposed axially on either side of the annular inner groove, the front and rear main sealing gaskets (26, 27) being configured to tightly cooperate with a first shank portion (14.1) of the shank, - a rear backup sealing gasket which is annular and which extends around the shank, the rear backup sealing gasket being located at the rear of the rear main sealing gasket and being fastened to the fluid injection portion, the rear backup sealing gasket being configured to tightly cooperate with a second shank portion (14.2) of the shank, - a leakage passage which is defined between the shank and the fluid injection portion, a leakage flow being intended to flow in the leakage passage in case of injection fluid leakage at the rear main sealing gasket, - at least one fluid discharge orifice which is provided on the fluid injection portion and which is fluidly connected to the leakage passage, the at least one fluid discharge orifice being configured to discharge the leakage flow flowing in the leakage passage outwardly of the hydraulic rotary-percussive hammer drill, characterized in that the leakage passage extends from the rear main sealing gasket up to the rear backup sealing gasket, and in that the first shank portion (14.1) is generally cylindrical and has a first outer diameter, and the second shank portion (14.2) is generally cylindrical and has a second outer diameter which is strictly larger than the first outer diameter, and in that the hydraulic rotary-percussive hammer drill includes pressure drop generation means disposed in the leakage passage and configured to generate pressure drops in the leakage passage when a leakage flow flows in the leakage passage, the pressure drop generation means including a deflection surface provided on the shank and located between the first shank portion (14.1) and the second shank portion (14.2), the deflection surface being configured to divert a leakage flow, flowing in the leakage passage towards the rear backup sealing gasket, in a flow direction which is transverse to the longitudinal axis of the shank. - a hammer drill body, - a fluid injection portion provided on a front portion of the hammer drill body, the fluid injection portion comprising a longitudinal passage, a fluid feed-in inlet intended to be fluidly connected to an injection fluid source and an annular inner groove fluidly connected to the fluid feed-in inlet and opening into the longitudinal passage, - a shank intended to be coupled to at least one drill bar equipped with a tool, the shank having a longitudinal axis and extending in the longitudinal passage of the fluid injection portion, the annular inner groove extending around the shank, the shank including a fluid injection conduit extending over at least a portion of the length of the shank and a communication orifice configured to fluidly connect the annular inner groove and the fluid injection conduit, - a striking piston slidably mounted inside the hammer drill body along a striking axis and configured to hit the shank, - a front main sealing gasket and a rear main sealing gasket which are annular and each extending around the shank, the front and rear main sealing gaskets (26, 27) being fastened to the fluid injection portion and being disposed axially on either side of the annular inner groove, the front and rear main sealing gaskets (26, 27) being configured to tightly cooperate with a first shank portion (14.1) of the shank, - a rear backup sealing gasket which is annular and which extends around the shank, the rear backup sealing gasket being located at the rear of the rear main sealing gasket and being fastened to the fluid injection portion, the rear backup sealing gasket being configured to tightly cooperate with a second shank portion (14.2) of the shank, - a leakage passage which is defined between the shank and the fluid injection portion, a leakage flow being intended to flow in the leakage passage in case of injection fluid leakage at the rear main sealing gasket, - at least one fluid discharge orifice which is provided on the fluid injection portion and which is fluidly connected to the leakage passage, the at least one fluid discharge orifice being configured to discharge the leakage flow flowing in the leakage passage outwardly of the hydraulic rotary-percussive hammer drill,