A telescopic gutter for a roof window comprising - at least two segments (1a, 1b, 1c, 2a, 2b), connected together by one fitting into the other, and the gutter is arranged to be mounted above the roof window and fixed to a roof, wherein said segments (1a, 1b, 1c, 2a, 2b) are thin-walled and made of a pliable material and each comprises a flat mounting plate (11, 21), a drainage channel (12, 22) and an outer section (13, 23) being an extension of said drainage channel, where said segments comprise identical dimensions in the transversal cross-section - and the drainage channel is arranged to be bent into the shape of a circular arc or into a polygonal shape, wherein - the arc-shaped drainage channel cross-section comprises a centre angle ( α) larger than the straight angle, preferably from 185 to 200 degrees, particularly 190 degrees, and the outer section of the arc shaped drainage channel is, located in a plane tangent to the arc-shaped drainage channel at the end point of its curve, - or the polygonal cross section of the drainage channel comprises at least three sections and at least the last of the three sections of the polygonal drainage channel is positioned so that the free edge of this last section is closer to the mounting plate than the connection of this last section with its adjacent section of the drainage channel, - while the distance between the end points of the drainage channel's cross-section (B12, B13, B23) and the mounting plate (11, 21) is shorter than the inner width (B1, B2) of the drainage channel (12, 22) wherein the segments ( 1a, 1b, 2a, 2b) are arranged to overlap each other on a section L and in said section L the segments ( 1a, 1b, 2a, 2b) are deformed within the extent of their elasticity and are arranged to form a pressure-fit connection with each other, wherein the free ends of the outer or last sections (13; 23) of both segments slightly protrude from each other such that a space extending in the width deirection of the channel (12, 22) is formed between said free ends of said outer or last sections of both segments ( 1a, 1b, 1c, 2a, 2b). - at least two segments (1a, 1b, 1c, 2a, 2b), connected together by one fitting into the other, and the gutter is arranged to be mounted above the roof window and fixed to a roof, wherein said segments (1a, 1b, 1c, 2a, 2b) are thin-walled and made of a pliable material and each comprises a flat mounting plate (11, 21), a drainage channel (12, 22) and an outer section (13, 23) being an extension of said drainage channel, where said segments comprise identical dimensions in the transversal cross-section - and the drainage channel is arranged to be bent into the shape of a circular arc or into a polygonal shape, wherein - the arc-shaped drainage channel cross-section comprises a centre angle ( α) larger than the straight angle, preferably from 185 to 200 degrees, particularly 190 degrees, and the outer section of the arc shaped drainage channel is, located in a plane tangent to the arc-shaped drainage channel at the end point of its curve, - or the polygonal cross section of the drainage channel comprises at least three sections and at least the last of the three sections of the polygonal drainage channel is positioned so that the free edge of this last section is closer to the mounting plate than the connection of this last section with its adjacent section of the drainage channel, - while the distance between the end points of the drainage channel's cross-section (B12, B13, B23) and the mounting plate (11, 21) is shorter than the inner width (B1, B2) of the drainage channel (12, 22) wherein the segments ( 1a, 1b, 2a, 2b) are arranged to overlap each other on a section L and in said section L the segments ( 1a, 1b, 2a, 2b) are deformed within the extent of their elasticity and are arranged to form a pressure-fit connection with each other, wherein the free ends of the outer or last sections (13; 23) of both segments slightly protrude from each other such that a space extending in the width deirection of the channel (12, 22) is formed between said free ends of said outer or last sections of both segments ( 1a, 1b, 1c, 2a, 2b).