A self-adjusting side guide for a document-handling machine having a feed deck along which documents are transported is provided. The self-adjusting side guide includes a first member mounted for movement along the feed deck toward and away from the documents; a guide wall mechanism operatively connected to the first member for movement relative to the first member; and a biasing device that applies a biasing force that biases the guide wall into a first position relative to the first member. The side guide operates such that at times when an external force sufficient to move the first member along the feed deck in the direction of the documents is applied to the guide wall mechanism, the guide wall mechanism moves toward the documents against the biasing force from the first position to a second position relative to the first member without any movement of the first member toward the documents.