diff --git a/src/nvim/api/buffer.c b/src/nvim/api/buffer.c
index 665c622c98..ebc9aeb75f 100644
--- a/src/nvim/api/buffer.c
+++ b/src/nvim/api/buffer.c
@@ -516,7 +516,7 @@ void nvim_buf_set_lines(uint64_t channel_id,
               kExtmarkNOOP);
 
   extmark_splice(curbuf, (int)start-1, 0, (int)(end-start), 0,
-                 deleted_bytes, (int)(end+extra-1), 0, inserted_bytes,
+                 deleted_bytes, (int)new_len, 0, inserted_bytes,
                  kExtmarkUndo);
 
   changed_lines((linenr_T)start, 0, (linenr_T)end, (long)extra, true);
diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index ca68ef04b0..0ed116c17f 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -6307,7 +6307,7 @@ bcount_t get_region_bytecount(buf_T *buf, linenr_T start_lnum,
                               linenr_T end_lnum, colnr_T start_col,
                               colnr_T end_col)
 {
-  linenr_T max_lnum = buf->b_ml.ml_line_lnum;
+  linenr_T max_lnum = buf->b_ml.ml_line_count;
   if (start_lnum > max_lnum) {
     return 0;
   }