diff --git a/NEWS.md b/NEWS.md
index 0fd950dcf6..7b0fdb280d 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -5,7 +5,7 @@
 * Fixed regression where `draw_key_rect()` stopped using `fill` colours 
   (@mitchelloharawild, #6609).
 * Fixed regression where `scale_{x,y}_*()` threw an error when an expression
-  object is set to `labels` argument (@yutannihilation, #6617).
+  object is set to `labels` argument (@yutannihilation, #6617, #6638).
 
 
 * Allow `stat` in `geom_hline`, `geom_vline`, and `geom_abline`. (@sierrajohnson, #6559)
diff --git a/R/scale-.R b/R/scale-.R
index df2046c25e..672328686f 100644
--- a/R/scale-.R
+++ b/R/scale-.R
@@ -1190,7 +1190,7 @@ ScaleContinuous <- ggproto("ScaleContinuous", Scale,
       labels <- lapply(labels, `[`, 1)
     }
     if (is.expression(labels)) {
-      labels <- as.list(labels)
+      labels <- as.list(unclass(labels))
     }
 
     labels
@@ -1438,7 +1438,7 @@ ScaleDiscrete <- ggproto("ScaleDiscrete", Scale,
     }
 
     if (is.expression(labels)) {
-      labels <- as.list(labels)
+      labels <- as.list(unclass(labels))
     }
     labels
   },
@@ -1689,7 +1689,7 @@ ScaleBinned <- ggproto("ScaleBinned", Scale,
       )
     }
     if (is.expression(labels)) {
-      labels <- as.list(labels)
+      labels <- as.list(unclass(labels))
     }
     labels
   },
diff --git a/tests/testthat/test-scales-breaks-labels.R b/tests/testthat/test-scales-breaks-labels.R
index 70a7e0ddcb..893ce2bfc6 100644
--- a/tests/testthat/test-scales-breaks-labels.R
+++ b/tests/testthat/test-scales-breaks-labels.R
@@ -18,10 +18,14 @@ test_that("labels don't have to match null breaks", {
 
 test_that("labels accept expressions", {
   labels <- parse(text = paste0(1:4, "^degree"))
-  sc <- scale_y_continuous(breaks = 1:4, labels = labels, limits = c(1, 3))
+  sc1 <- scale_y_continuous(breaks = 1:4, labels = labels, limits = c(1, 3))
 
-  expect_equal(sc$get_breaks(), 1:4)
-  expect_equal(sc$get_labels(), as.list(labels))
+  # classed labels should also work (#6638)
+  classed_labels <- structure(labels, class = "foo")
+  sc2 <- scale_y_continuous(breaks = 1:4, labels = classed_labels, limits = c(1, 3))
+
+  expect_equal(sc1$get_labels(), as.list(labels))
+  expect_equal(sc2$get_labels(), as.list(labels))
 })
 
 test_that("labels don't have extra spaces", {