diff --git a/src/cairo-bentley-ottmann-rectangular.c b/src/cairo-bentley-ottmann-rectangular.c
index 5541bdc..a6e8c31 100644
--- a/src/cairo-bentley-ottmann-rectangular.c
+++ b/src/cairo-bentley-ottmann-rectangular.c
@@ -554,8 +554,10 @@ sweep_line_delete_edge (sweep_line_t *sweep, edge_t *edge)
     if (sweep->cursor == edge)
 	sweep->cursor = edge->prev;
 
-    edge->prev->next = edge->next;
-    edge->next->prev = edge->prev;
+    if (edge->prev)
+        edge->prev->next = edge->next;
+    if (edge->next)
+        edge->next->prev = edge->prev;
 }
 
 static inline cairo_bool_t
@@ -565,6 +567,7 @@ sweep_line_delete (sweep_line_t	*sweep, rectangle_t *rectangle)
 
     update = TRUE;
     if (sweep->fill_rule == CAIRO_FILL_RULE_WINDING &&
+        rectangle->left.prev &&
 	rectangle->left.prev->dir == rectangle->left.dir)
     {
 	update = rectangle->left.next != &rectangle->right;