diff --git a/sys/uvm/uvm_map.c b/sys/uvm/uvm_map.c
index 46b829b478a6..30b5d73dc6f6 100644
--- a/sys/uvm/uvm_map.c
+++ b/sys/uvm/uvm_map.c
@@ -1994,7 +1994,20 @@ uvm_map_findspace(struct vm_map *map, vaddr_t hint, vsize_t length,
 	/* Try to find the space in the red-black tree */
 
 	/* Check slot before any entry */
-	hint = topdown ? entry->next->start - length : entry->end;
+	if (topdown) {
+		KASSERTMSG(entry->next->start >= vm_map_min(map),
+		    "map=%p entry=%p entry->next=%p"
+		    " entry->next->start=0x%"PRIxVADDR" min=0x%"PRIxVADDR,
+		    map, entry, entry->next,
+		    entry->next->start, vm_map_min(map));
+		if (length > entry->next->start - vm_map_min(map))
+			hint = vm_map_min(map); /* XXX goto wraparound? */
+		else
+			hint = entry->next->start - length;
+		KASSERT(hint >= vm_map_min(map));
+	} else {
+		hint = entry->end;
+	}
 	INVARIANTS();
 	avail = uvm_map_space_avail(&hint, length, uoffset, align, flags,
 	    topdown, entry);