diff --git a/NEWS.md b/NEWS.md
index 8fe979a6a8..b6bd30f1db 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -77,6 +77,8 @@
     * `guide_coloursteps()` and `guide_bins()` sort breaks (#5152).
     * `guide_axis()` gains a `cap` argument that can be used to trim the
       axis line to extreme breaks (#4907).
+    * `guide_colourbar()` and `guide_coloursteps()` merge properly when one
+      of aesthetics is dropped (#5324).
     * Fixed regression in `guide_legend()` where the `linewidth` key size
       wasn't adapted to the width of the lines (#5160).
 
diff --git a/R/guide-colorbar.R b/R/guide-colorbar.R
index 092b5a35ba..4917679ebf 100644
--- a/R/guide-colorbar.R
+++ b/R/guide-colorbar.R
@@ -376,6 +376,8 @@ GuideColourbar <- ggproto(
   },
 
   merge = function(self, params, new_guide, new_params) {
+    new_params$key$.label <- new_params$key$.value <- NULL
+    params$key <- vec_cbind(params$key, new_params$key)
     return(list(guide = self, params = params))
   },
 
diff --git a/tests/testthat/test-guides.R b/tests/testthat/test-guides.R
index a19de230b6..ac704fdf79 100644
--- a/tests/testthat/test-guides.R
+++ b/tests/testthat/test-guides.R
@@ -307,6 +307,27 @@ test_that("guide_coloursteps and guide_bins return ordered breaks", {
   expect_true(all(diff(key$.value) < 0))
 })
 
+
+test_that("guide_colourbar merging preserves both aesthetics", {
+  # See issue 5324
+
+  scale1 <- scale_colour_viridis_c()
+  scale1$train(c(0, 2))
+
+  scale2 <- scale_fill_viridis_c()
+  scale2$train(c(0, 2))
+
+  g <- guide_colourbar()
+  p <- g$params
+
+  p1 <- g$train(p, scale1, "colour")
+  p2 <- g$train(p, scale2, "fill")
+
+  merged <- g$merge(p1, g, p2)
+
+  expect_true(all(c("colour", "fill") %in% names(merged$params$key)))
+})
+
 test_that("guide_colourbar warns about discrete scales", {
 
   g <- guide_colourbar()
@@ -315,6 +336,7 @@ test_that("guide_colourbar warns about discrete scales", {
 
   expect_warning(g <- g$train(g$params, s, "colour"), "needs continuous scales")
   expect_null(g)
+
 })
 
 # Visual tests ------------------------------------------------------------