Index: machdep.c
===================================================================
RCS file: /cvs/src/sys/arch/sparc64/sparc64/machdep.c,v
diff -u -p -r1.218 machdep.c
--- machdep.c	22 May 2024 05:51:49 -0000	1.218
+++ machdep.c	7 Sep 2024 00:36:21 -0000
@@ -991,12 +991,20 @@ _bus_dmamap_load_mbuf(bus_dma_tag_t t, b
 			buflen -= incr;
 			vaddr += incr;
 
-			if (i > 0 && pa == (segs[i - 1].ds_addr +
-			    segs[i - 1].ds_len) && ((segs[i - 1].ds_len + incr)
-			    < map->_dm_maxsegsz)) {
-				/* Hey, waddyaknow, they're contiguous */
-				segs[i - 1].ds_len += incr;
-				continue;
+			if (i > 0) {
+				bus_dma_segment_t *pseg = &segs[i - 1];
+				if (pa == pseg->ds_addr + pseg->ds_len) {
+					/* waddyaknow, they're contiguous */
+					long nlen = pseg->ds_len + incr;
+					if (nlen <= map->_dm_maxsegsz) {
+						pseg->ds_len = nlen;
+						continue;
+					}
+					pseg->ds_len = map->_dm_maxsegsz;
+
+					pa = pseg->ds_addr + map->_dm_maxsegsz;
+					incr = nlen - map->_dm_maxsegsz;
+				}
 			}
 			segs[i].ds_addr = pa;
 			segs[i].ds_len = incr;