An inkjet printing system comprising an apparatus for defect detection in a printing system, comprising: a sensing unit comprising at least one first sensor device for sensing a surface geometry or topology of a sheet to be printed as the sheet travels on a transport path of the printing system, the transport path comprising a simplex path (Ps) and a duplex path (P D), and for generating data representative of that surface geometry or topology, wherein the sensing unit is arranged, such that sheets input on the simplex path (Ps) and sheets returning on the duplex path (P D) pass via the sensing unit; a processor device for processing the data from the first sensor device to detect and classify deformations in the surface geometry or topology of the sheet; and a controller for controlling further progress of the sheet along the transport path of the printing system in dependence upon the deformations in the surface geometry or topology of the sheet detected and classified by the processor device, wherein the controller is configured to control and/or operate a removal device for removing the sheet from the transport path of the printing system if and when the processor device detects at least one deformations in the surface geometry or topology of the sheet that would render the sheet unsuitable for printing, wherein the apparatus includes said removal device, characterized in that: the controller is further configured, when a first sheet is part of a print job for a plurality of sheets, for inserting a second sheet in a relative position of the first sheet in the plurality of sheets on the transport path of the printing system, i.e. by positioning the second sheet in the correct order of the print job, when the removal device removed said first sheet from the transport path of the printing system, which first sheet has been printed on its first or simplex side with a first image in a first or simplex pass and which first sheet is to be printed on its second or duplex side with a second image on a second or duplex pass; and for operating the image forming unit to print the first image and the second image on the respective sides of the second sheet. a sensing unit comprising at least one first sensor device for sensing a surface geometry or topology of a sheet to be printed as the sheet travels on a transport path of the printing system, the transport path comprising a simplex path (Ps) and a duplex path (P D), and for generating data representative of that surface geometry or topology, wherein the sensing unit is arranged, such that sheets input on the simplex path (Ps) and sheets returning on the duplex path (P D) pass via the sensing unit; a processor device for processing the data from the first sensor device to detect and classify deformations in the surface geometry or topology of the sheet; and a controller for controlling further progress of the sheet along the transport path of the printing system in dependence upon the deformations in the surface geometry or topology of the sheet detected and classified by the processor device, wherein the controller is configured to control and/or operate a removal device for removing the sheet from the transport path of the printing system if and when the processor device detects at least one deformations in the surface geometry or topology of the sheet that would render the sheet unsuitable for printing, wherein the apparatus includes said removal device, the controller is further configured, when a first sheet is part of a print job for a plurality of sheets, for inserting a second sheet in a relative position of the first sheet in the plurality of sheets on the transport path of the printing system, i.e. by positioning the second sheet in the correct order of the print job, when the removal device removed said first sheet from the transport path of the printing system, which first sheet has been printed on its first or simplex side with a first image in a first or simplex pass and which first sheet is to be printed on its second or duplex side with a second image on a second or duplex pass; and for operating the image forming unit to print the first image and the second image on the respective sides of the second sheet.