diff --git a/NEWS.md b/NEWS.md
index 28ecb99196..f9bdc996e0 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* Fixed bug in `stat_function()` so x-axis title now produced automatically 
+  when no data added. (@phispu, #5647).
 * geom_sf now accepts shape names (@sierrajohnson, #5808)
 * Added `gg` class to `labs()` (@phispu, #5553).
 * Missing values from discrete palettes are no longer translated 
diff --git a/R/stat-function.R b/R/stat-function.R
index 8f31b8daba..bf6d2e4b74 100644
--- a/R/stat-function.R
+++ b/R/stat-function.R
@@ -50,7 +50,7 @@ stat_function <- function(mapping = NULL, data = NULL,
 #' @usage NULL
 #' @export
 StatFunction <- ggproto("StatFunction", Stat,
-  default_aes = aes(y = after_scale(y)),
+  default_aes = aes(x = NULL, y = after_scale(y)),
 
   compute_group = function(data, scales, fun, xlim = NULL, n = 101, args = list()) {
     if (is.null(scales$x)) {