diff --git a/DESCRIPTION b/DESCRIPTION
index c7d7dc84..c0993844 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Type: Package
 Package: flextable
 Title: Functions for Tabular Reporting
-Version: 0.9.7.003
+Version: 0.9.7.004
 Authors@R: c(
     person("David", "Gohel", , "david.gohel@ardata.fr", role = c("aut", "cre")),
     person("ArData", role = "cph"),
diff --git a/NEWS.md b/NEWS.md
index 36d6c54d..a2bc4b4b 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -4,6 +4,7 @@
 
 - fix caption issue that came with no version of bookdown (issue #645),
 'bookdown' management of caption has been simplified.
+- fix vertical overlapping lines with grid output (issue #644)
 
 # flextable 0.9.6
 
diff --git a/R/grid_funs.R b/R/grid_funs.R
index 8c9b0dc4..8924dd15 100644
--- a/R/grid_funs.R
+++ b/R/grid_funs.R
@@ -135,6 +135,10 @@ grid_data_add_cell_info <- function(grid_data, x) {
       "border.color.right", "border.width.top", "border.width.bottom"
     )
   ]
+  # apply a correction to overlapping vert. borders
+  setorderv(fortify_borders_data, cols = c(".part", ".row_id", ".col_id"))
+  fortify_borders_data[fortify_borders_data$border.width.right == shift(fortify_borders_data$border.width.left, type = "lead", fill = -1),
+     c("border.width.right") := 0, by = c(".part", ".row_id")]
 
   cell_data <- cell_data[, .SD,
     .SDcols =