diff --git a/NEWS.md b/NEWS.md
index 2369989eb2..2076f813df 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -67,6 +67,11 @@
 * Updated documentation for `geom_contour()` to correctly reflect argument 
 precedence between `bins` and `binwidth`. (@eliocamp, #4651)
 
+* The `ticks.linewidth` and `frame.linewidth` parameters of `guide_colourbar()`
+  are now multiplied with `.pt` like elsewhere in ggplot2. It can cause visual
+  changes when these arguments are not the defaults and these changes can be 
+  restored to their previous behaviour by adding `/ .pt` (@teunbrand #4314).
+
 * Dots in `geom_dotplot()` are now correctly aligned to the baseline when
   `stackratio != 1` and `stackdir != "up"` (@mjskay, #4614)
 
diff --git a/R/guide-colorbar.r b/R/guide-colorbar.r
index 5c933fa5f0..b65e316b48 100644
--- a/R/guide-colorbar.r
+++ b/R/guide-colorbar.r
@@ -21,7 +21,7 @@
 #' @param frame.colour A string specifying the colour of the frame
 #'   drawn around the bar. If `NULL` (the default), no frame is drawn.
 #' @param frame.linewidth A numeric specifying the width of the frame
-#'   drawn around the bar.
+#'   drawn around the bar in millimetres.
 #' @param frame.linetype A numeric specifying the linetype of the frame
 #'   drawn around the bar.
 #' @param nbin A numeric specifying the number of bins for drawing the
@@ -33,7 +33,8 @@
 #' @param ticks A logical specifying if tick marks on the colourbar should be
 #'   visible.
 #' @param ticks.colour A string specifying the colour of the tick marks.
-#' @param ticks.linewidth A numeric specifying the width of the tick marks.
+#' @param ticks.linewidth A numeric specifying the width of the tick marks in
+#'   millimetres.
 #' @param draw.ulim A logical specifying if the upper limit tick marks should
 #'   be visible.
 #' @param draw.llim A logical specifying if the lower limit tick marks should
@@ -125,13 +126,13 @@ guide_colourbar <- function(
 
   # frame
   frame.colour = NULL,
-  frame.linewidth = 0.5,
+  frame.linewidth = 0.5 / .pt,
   frame.linetype = 1,
 
   # ticks
   ticks = TRUE,
   ticks.colour = "white",
-  ticks.linewidth = 0.5,
+  ticks.linewidth = 0.5 / .pt,
   draw.ulim= TRUE,
   draw.llim = TRUE,
 
@@ -322,7 +323,7 @@ guide_gengrob.colorbar <- function(guide, theme) {
                     default.units = "cm",
                     gp = gpar(
                       col = guide$frame.colour,
-                      lwd = guide$frame.linewidth,
+                      lwd = guide$frame.linewidth * .pt,
                       lty = guide$frame.linetype,
                       fill = NA)
                     )
@@ -451,7 +452,7 @@ guide_gengrob.colorbar <- function(guide, theme) {
       default.units = "cm",
       gp = gpar(
         col = guide$ticks.colour,
-        lwd = guide$ticks.linewidth,
+        lwd = guide$ticks.linewidth * .pt,
         lineend = "butt"
       )
     )
diff --git a/man/guide_colourbar.Rd b/man/guide_colourbar.Rd
index e2a6252013..b00f6956c5 100644
--- a/man/guide_colourbar.Rd
+++ b/man/guide_colourbar.Rd
@@ -21,11 +21,11 @@ guide_colourbar(
   nbin = 300,
   raster = TRUE,
   frame.colour = NULL,
-  frame.linewidth = 0.5,
+  frame.linewidth = 0.5/.pt,
   frame.linetype = 1,
   ticks = TRUE,
   ticks.colour = "white",
-  ticks.linewidth = 0.5,
+  ticks.linewidth = 0.5/.pt,
   draw.ulim = TRUE,
   draw.llim = TRUE,
   direction = NULL,
@@ -52,11 +52,11 @@ guide_colorbar(
   nbin = 300,
   raster = TRUE,
   frame.colour = NULL,
-  frame.linewidth = 0.5,
+  frame.linewidth = 0.5/.pt,
   frame.linetype = 1,
   ticks = TRUE,
   ticks.colour = "white",
-  ticks.linewidth = 0.5,
+  ticks.linewidth = 0.5/.pt,
   draw.ulim = TRUE,
   draw.llim = TRUE,
   direction = NULL,
@@ -124,7 +124,7 @@ raster image.}
 drawn around the bar. If \code{NULL} (the default), no frame is drawn.}
 
 \item{frame.linewidth}{A numeric specifying the width of the frame
-drawn around the bar.}
+drawn around the bar in millimetres.}
 
 \item{frame.linetype}{A numeric specifying the linetype of the frame
 drawn around the bar.}
@@ -134,7 +134,8 @@ visible.}
 
 \item{ticks.colour}{A string specifying the colour of the tick marks.}
 
-\item{ticks.linewidth}{A numeric specifying the width of the tick marks.}
+\item{ticks.linewidth}{A numeric specifying the width of the tick marks in
+millimetres.}
 
 \item{draw.ulim}{A logical specifying if the upper limit tick marks should
 be visible.}
diff --git a/man/guide_coloursteps.Rd b/man/guide_coloursteps.Rd
index 2656d48d9d..98ed9c382c 100644
--- a/man/guide_coloursteps.Rd
+++ b/man/guide_coloursteps.Rd
@@ -31,11 +31,12 @@ the height of the colourbar. Default value is \code{legend.key.height} or
     \item{\code{frame.colour}}{A string specifying the colour of the frame
 drawn around the bar. If \code{NULL} (the default), no frame is drawn.}
     \item{\code{frame.linewidth}}{A numeric specifying the width of the frame
-drawn around the bar.}
+drawn around the bar in millimetres.}
     \item{\code{frame.linetype}}{A numeric specifying the linetype of the frame
 drawn around the bar.}
     \item{\code{ticks.colour}}{A string specifying the colour of the tick marks.}
-    \item{\code{ticks.linewidth}}{A numeric specifying the width of the tick marks.}
+    \item{\code{ticks.linewidth}}{A numeric specifying the width of the tick marks in
+millimetres.}
     \item{\code{draw.ulim}}{A logical specifying if the upper limit tick marks should
 be visible.}
     \item{\code{draw.llim}}{A logical specifying if the lower limit tick marks should
diff --git a/tests/testthat/test-guides.R b/tests/testthat/test-guides.R
index c2735c2e89..25960009cd 100644
--- a/tests/testthat/test-guides.R
+++ b/tests/testthat/test-guides.R
@@ -482,9 +482,9 @@ test_that("colorbar can be styled", {
           low = 'white', high = 'red',
           guide = guide_colorbar(
             frame.colour = "green",
-            frame.linewidth = 1.5,
+            frame.linewidth = 1.5 / .pt,
             ticks.colour = "black",
-            ticks.linewidth = 2.5
+            ticks.linewidth = 2.5 / .pt
             )
         )
     )