A header for an agricultural harvester, the header comprising: a frame; a cutter bar connected to the frame and configured to flex to accommodate changes in terrain as the harvester moves over the terrain; a lateral draper belt assembly connected to the frame, the lateral draper belt assembly including: a plurality of rollers (304A, 304B); an endless web circumscribing the plurality of rollers (304A, 304B) and defining an inner surface and an outer surface, the endless web being configured to flex to accommodate flexing from the cutter bar; and, wherein the header further comprises a guide assembly comprising: a first elongated guide connected to the frame and configured to extend over the outer surface of an endless web, and a second elongated guide (602A, 602B, 602C) connected to the frame and configured to extend from the inner surface of the endless web, characterised in that the first elongated guide having a slot for receiving a first complementary shaped draper belt portion, the first complementary shaped draper belt portion defined as a first elongated tongue extending from the outer surface of the endless web adjacent a front edge of the endless web; and, the second elongated guide (602A, 602B, 602C) having a slot for receiving a second complementary shaped draper belt portion (600A, 600B, 600C), the second complementary shaped draper belt portion (600A, 600B, 600C) defined as a second elongated tongue (600A, 600B, 600C) extending from the inner surface of the endless web. a frame; a cutter bar connected to the frame and configured to flex to accommodate changes in terrain as the harvester moves over the terrain; a lateral draper belt assembly connected to the frame, the lateral draper belt assembly including: a plurality of rollers (304A, 304B); an endless web circumscribing the plurality of rollers (304A, 304B) and defining an inner surface and an outer surface, the endless web being configured to flex to accommodate flexing from the cutter bar; and, wherein the header further comprises a guide assembly comprising: a first elongated guide connected to the frame and configured to extend over the outer surface of an endless web, and a second elongated guide (602A, 602B, 602C) connected to the frame and configured to extend from the inner surface of the endless web, characterised in that the first elongated guide having a slot for receiving a first complementary shaped draper belt portion, the first complementary shaped draper belt portion defined as a first elongated tongue extending from the outer surface of the endless web adjacent a front edge of the endless web; and, the second elongated guide (602A, 602B, 602C) having a slot for receiving a second complementary shaped draper belt portion (600A, 600B, 600C), the second complementary shaped draper belt portion (600A, 600B, 600C) defined as a second elongated tongue (600A, 600B, 600C) extending from the inner surface of the endless web. a plurality of rollers (304A, 304B); an endless web circumscribing the plurality of rollers (304A, 304B) and defining an inner surface and an outer surface, the endless web being configured to flex to accommodate flexing from the cutter bar; and, wherein the header further comprises a guide assembly comprising: a first elongated guide connected to the frame and configured to extend over the outer surface of an endless web, and a second elongated guide (602A, 602B, 602C) connected to the frame and configured to extend from the inner surface of the endless web, characterised in that the first elongated guide having a slot for receiving a first complementary shaped draper belt portion, the first complementary shaped draper belt portion defined as a first elongated tongue extending from the outer surface of the endless web adjacent a front edge of the endless web; and, the second elongated guide (602A, 602B, 602C) having a slot for receiving a second complementary shaped draper belt portion (600A, 600B, 600C), the second complementary shaped draper belt portion (600A, 600B, 600C) defined as a second elongated tongue (600A, 600B, 600C) extending from the inner surface of the endless web. a first elongated guide connected to the frame and configured to extend over the outer surface of an endless web, and a second elongated guide (602A, 602B, 602C) connected to the frame and configured to extend from the inner surface of the endless web, characterised in that the first elongated guide having a slot for receiving a first complementary shaped draper belt portion, the first complementary shaped draper belt portion defined as a first elongated tongue extending from the outer surface of the endless web adjacent a front edge of the endless web; and, the second elongated guide (602A, 602B, 602C) having a slot for receiving a second complementary shaped draper belt portion (600A, 600B, 600C), the second complementary shaped draper belt portion (600A, 600B, 600C) defined as a second elongated tongue (600A, 600B, 600C) extending from the inner surface of the endless web.