diff --git a/R/plot.R b/R/plot.R
index 47fec471a77..0836cbd0cf3 100644
--- a/R/plot.R
+++ b/R/plot.R
@@ -57,6 +57,10 @@
 #'   the marked vertex groups. It is in the same units as the vertex sizes. If a
 #'   vector is given, then different values are used for the different vertex
 #'   groups.
+#' @param mark.lwd A numeric scalar or vector, the linewidth of the border around
+#'   the marked vertex groups.  If a
+#'   vector is given, then different values are used for the different vertex
+#'   groups.
 #' @param loop.size A numeric scalar that allows the user to scale the loop edges
 #'   of the network. The default loop size is 1. Larger values will produce larger
 #'   loops.
@@ -92,6 +96,7 @@ plot.igraph <- function(
   mark.col = rainbow(length(mark.groups), alpha = 0.3),
   mark.border = rainbow(length(mark.groups), alpha = 1),
   mark.expand = 15,
+  mark.lwd = 1,
   loop.size = 1,
   ...
 ) {
@@ -252,6 +257,7 @@ plot.igraph <- function(
   mark.border <- rep(mark.border, length.out = length(mark.groups))
   mark.col <- rep(mark.col, length.out = length(mark.groups))
   mark.expand <- rep(mark.expand, length.out = length(mark.groups))
+  mark.lwd <- rep(mark.lwd, length.out = length(mark.groups))
 
   for (g in seq_along(mark.groups)) {
     .members <- mark.groups[[g]]
@@ -267,7 +273,8 @@ plot.igraph <- function(
       expand.by = mark.expand[g] / 200,
       shape = mark.shape[g],
       col = mark.col[g],
-      border = mark.border[g]
+      border = mark.border[g],
+      border.lwd = mark.lwd[g]
     )
   }
 
@@ -1776,7 +1783,8 @@ igraph.polygon <- function(
   expand.by = 15 / 200,
   shape = 1 / 2,
   col = "#ff000033",
-  border = NA
+  border = NA,
+  border.lwd = 1
 ) {
   by <- expand.by
   pp <- rbind(
@@ -1788,5 +1796,13 @@ igraph.polygon <- function(
   )
 
   cl <- convex_hull(pp)
-  xspline(cl$rescoords, shape = shape, open = FALSE, col = col, border = border)
+
+  xspline(
+    cl$rescoords,
+    shape = shape,
+    open = FALSE,
+    col = col,
+    border = border,
+    lwd = border.lwd
+  )
 }
diff --git a/man/plot.igraph.Rd b/man/plot.igraph.Rd
index 36451e890b8..c1ee1232a98 100644
--- a/man/plot.igraph.Rd
+++ b/man/plot.igraph.Rd
@@ -16,6 +16,7 @@
   mark.col = rainbow(length(mark.groups), alpha = 0.3),
   mark.border = rainbow(length(mark.groups), alpha = 1),
   mark.expand = 15,
+  mark.lwd = 1,
   loop.size = 1,
   ...
 )
@@ -58,6 +59,11 @@ the marked vertex groups. It is in the same units as the vertex sizes. If a
 vector is given, then different values are used for the different vertex
 groups.}
 
+\item{mark.lwd}{A numeric scalar or vector, the linewidth of the border around
+the marked vertex groups.  If a
+vector is given, then different values are used for the different vertex
+groups.}
+
 \item{loop.size}{A numeric scalar that allows the user to scale the loop edges
 of the network. The default loop size is 1. Larger values will produce larger
 loops.}
diff --git a/tests/testthat/_snaps/plot/mark-border-lwd.svg b/tests/testthat/_snaps/plot/mark-border-lwd.svg
new file mode 100644
index 00000000000..2bf2b3a917d
--- /dev/null
+++ b/tests/testthat/_snaps/plot/mark-border-lwd.svg
@@ -0,0 +1,40 @@
+<?xml version='1.0' encoding='UTF-8' ?>
+<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' class='svglite' data-engine-version='2.0' width='720.00pt' height='576.00pt' viewBox='0 0 720.00 576.00'>
+<defs>
+  <style type='text/css'><![CDATA[
+    .svglite line, .svglite polyline, .svglite polygon, .svglite path, .svglite rect, .svglite circle {
+      fill: none;
+      stroke: #000000;
+      stroke-linecap: round;
+      stroke-linejoin: round;
+      stroke-miterlimit: 10.00;
+    }
+  ]]></style>
+</defs>
+<rect width='100%' height='100%' style='stroke: none; fill: #FFFFFF;'/>
+<defs>
+  <clipPath id='cpMC4wMHw3MjAuMDB8MC4wMHw1NzYuMDA='>
+    <rect x='0.00' y='0.00' width='720.00' height='576.00' />
+  </clipPath>
+</defs>
+<g clip-path='url(#cpMC4wMHw3MjAuMDB8MC4wMHw1NzYuMDA=)'>
+</g>
+<defs>
+  <clipPath id='cpNTkuMDR8Njg5Ljc2fDU5LjA0fDUwMi41Ng=='>
+    <rect x='59.04' y='59.04' width='630.72' height='443.52' />
+  </clipPath>
+</defs>
+<g clip-path='url(#cpNTkuMDR8Njg5Ljc2fDU5LjA0fDUwMi41Ng==)'>
+<polygon points='276.62,407.91 247.29,378.58 247.29,183.02 276.62,153.69 472.18,153.69 501.51,183.02 501.51,378.58 472.18,407.91 ' style='stroke-width: 3.75; stroke: #FF0000; fill: #FF0000; fill-opacity: 0.30;' />
+<line x1='286.40' y1='378.58' x2='462.40' y2='378.58' style='stroke-width: 0.075;' />
+<line x1='283.54' y1='371.66' x2='465.26' y2='189.94' style='stroke-width: 0.075;' />
+<line x1='276.62' y1='368.80' x2='276.62' y2='192.80' style='stroke-width: 0.075;' />
+<line x1='472.18' y1='368.80' x2='472.18' y2='192.80' style='stroke-width: 0.075;' />
+<line x1='465.26' y1='371.66' x2='283.54' y2='189.94' style='stroke-width: 0.075;' />
+<line x1='462.40' y1='183.02' x2='286.40' y2='183.02' style='stroke-width: 0.075;' />
+<circle cx='276.62' cy='378.58' r='9.78' style='stroke-width: 0.75; fill: #E69F00;' />
+<circle cx='472.18' cy='378.58' r='9.78' style='stroke-width: 0.75; fill: #E69F00;' />
+<circle cx='472.18' cy='183.02' r='9.78' style='stroke-width: 0.75; fill: #E69F00;' />
+<circle cx='276.62' cy='183.02' r='9.78' style='stroke-width: 0.75; fill: #E69F00;' />
+</g>
+</svg>
diff --git a/tests/testthat/test-plot.R b/tests/testthat/test-plot.R
index 171f6bb7568..106bdeb0546 100644
--- a/tests/testthat/test-plot.R
+++ b/tests/testthat/test-plot.R
@@ -154,3 +154,26 @@ test_that("Arrow drawing works correctly", {
   }
   vdiffr::expect_doppelganger("standard-arrow-sizes", standard_arrow_sizes)
 })
+
+test_that("mark border linewidth", {
+  skip_if_not_installed("vdiffr")
+  mark_border_lwd <- function() {
+    g <- make_full_graph(4, directed = FALSE)
+    V(g)$x <- c(1, 2, 2, 1)
+    V(g)$y <- c(1, 1, 2, 2)
+    wc <- cluster_walktrap(g)
+    plot(
+      wc,
+      g,
+      vertex.label = NA,
+      vertex.size = 20,
+      mark.shape = 0,
+      edge.width = 0.1,
+      mark.expand = 40,
+      mark.lwd = 5,
+      margin = 1
+    )
+  }
+
+  vdiffr::expect_doppelganger("mark-border-lwd", mark_border_lwd)
+})