diff --git a/R/labels.R b/R/labels.R
index 309f38902e..09f0490759 100644
--- a/R/labels.R
+++ b/R/labels.R
@@ -80,10 +80,17 @@ setup_plot_labels <- function(plot, layers, data) {
   extra_labels <- setdiff(names(plot_labels), known_labels)
 
   if (length(extra_labels) > 0) {
-    extra_labels <- paste0(
-      "{.code ", extra_labels, " = \"", plot_labels[extra_labels], "\"}"
+
+    warn_labels <- plot_labels[extra_labels]
+    warn_labels <- ifelse(
+      vapply(warn_labels, is.function, logical(1)),
+      "{.cls function}",
+      paste0("{.val ", warn_labels, "}")
     )
+
+    extra_labels <- paste0("{.field ", extra_labels, "} : ", warn_labels)
     names(extra_labels) <- rep("*", length(extra_labels))
+
     cli::cli_warn(c(
       "Ignoring unknown labels:",
       extra_labels
diff --git a/tests/testthat/_snaps/labels.md b/tests/testthat/_snaps/labels.md
index 2a4bd75ff4..dcbcfe974f 100644
--- a/tests/testthat/_snaps/labels.md
+++ b/tests/testthat/_snaps/labels.md
@@ -15,7 +15,9 @@
 # warnings are thrown for unknown labels
 
     Ignoring unknown labels:
-    * `foo = "bar"`
+    * foo : "i don't exist"
+    * bar : <function>
+    * qux : "expression(me * neither)"
 
 # plot.tag.position rejects invalid input
 
diff --git a/tests/testthat/test-labels.R b/tests/testthat/test-labels.R
index 4befce8af6..be947ee1c9 100644
--- a/tests/testthat/test-labels.R
+++ b/tests/testthat/test-labels.R
@@ -110,7 +110,13 @@ test_that("get_alt_text checks dots", {
 })
 
 test_that("warnings are thrown for unknown labels", {
-  p <- ggplot(mtcars, aes(mpg, disp)) + geom_point() + labs(foo = 'bar')
+  p <- ggplot(mtcars, aes(mpg, disp)) +
+    geom_point() +
+    labs(
+      foo = "i don't exist",
+      bar = function(x) "i don't exist either",
+      qux = expression(me * neither)
+    )
   expect_snapshot_warning(ggplot_build(p))
 })