An inclined position of a product, leaving a nip between two folding rollers of a longitudinal folding machine, is corrected. The product is pressed into the nip between the rollers by a folding blade that can be moved up and down relative to a folding table. The product thus leaves the nip between the rollers and is transported in a direction of transport. The time of passage of a leading or a trailing edge of a product is detected at two measurement points which are spaced apart from each other and which are arranged transversely to the direction of transport of the product to be folded. Based on the times of passage that are detected by the two measurement points, and on commutation and/or data processing techniques, a deviation between a time offset detected during the passage of the corresponding product edge at the two measurement points, and a nominal time offset, is determined and analyzed. In the event that the deviation exceeds at least a tolerance range, a measure is initiated, by the use of a control device, in order to act against the deviation. The measure that is to be taken is based on retaining the product to a greater or lesser extent when the product is passing the folding rollers and/or in the provision of more or less friction between the braking elements and the product.