diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index f03de3236c8d..598b74fb8fae 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -4938,6 +4938,12 @@ def scatter(self, x, y, s=None, c=None, marker=None, cmap=None, norm=None,
             marker_obj = marker
         else:
             marker_obj = mmarkers.MarkerStyle(marker)
+        if cbook._str_equal(marker_obj.get_marker(), ","):
+            _api.warn_external(
+                "The pixel maker ',' is not supported on scatter(); using "
+                "a finite-sized square instead, which is not necessarily 1 pixel in "
+                "size. Use the square marker 's' instead to suppress this warning."
+            )
 
         path = marker_obj.get_path().transformed(
             marker_obj.get_transform())