diff --git a/NEWS.md b/NEWS.md
index 1fba13fba8..13cfd1dde9 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -10,6 +10,8 @@
 * Patterns and gradients are now also enabled in `geom_sf()` 
   (@teunbrand, #5716).
 * `stat_bin()` deals with non-finite breaks better (@teunbrand, #5665).
+* When legends detect the presence of values in a layer, `NA` is now detected
+  if the data contains values outside the given breaks (@teunbrand, #5749).
 * `annotate()` now warns about `stat` or `position` arguments (@teunbrand, #5151)
 
 # ggplot2 3.5.0
diff --git a/R/guide-legend.R b/R/guide-legend.R
index afcde6744f..c685cdd8c7 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -649,6 +649,19 @@ keep_key_data <- function(key, data, aes, show) {
   for (column in match) {
     keep <- keep | key$.value %in% data[[column]]
   }
+
+  # NA might be included in breaks but originate from non-missing values that
+  # map to NA instead of *being* NA. We double-check if there are values
+  # outside the non-missing conventional limits.
+  is_na <- which(is.na(key$.value) & !keep)
+  if (length(is_na) > 0) {
+    na_keep <- FALSE
+    for (column in match) {
+      na_keep <- na_keep || !all(data[[column]] %in% key$.value)
+    }
+    keep[is_na] <- na_keep
+  }
+
   keep
 }
 
diff --git a/tests/testthat/test-draw-key.R b/tests/testthat/test-draw-key.R
index 6e6b84f093..223bfd6d5c 100644
--- a/tests/testthat/test-draw-key.R
+++ b/tests/testthat/test-draw-key.R
@@ -96,6 +96,11 @@ test_that("keep_draw_key", {
     c(FALSE, TRUE)
   )
 
+  # Missing values
+  key  <- data_frame0(.value = c("A", "B", NA))
+  data <- data_frame0(foo = c("A", "B", "C")) # 'C' should count as NA
+  expect_equal(keep_key_data(key, data, "foo", show = NA), c(TRUE, TRUE, TRUE))
+
   p <- ggplot(data.frame(x = 1:2), aes(x, x)) +
     geom_point(
       aes(colour = "point", alpha = "point"),