From cb2ae6df665701637398122ae224001ca521f1c8 Mon Sep 17 00:00:00 2001
From: Valentin Bruch <46252273+stiglers-eponym@users.noreply.github.com>
Date: Sun, 17 May 2026 03:47:39 +0200
Subject: [PATCH] Backport PR #31666: plt.stairs: fix unit handling for
 orientation="horizontal"

---
 lib/matplotlib/axes/_axes.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 687bb4b48d3b..b0ec08a78e75 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -7762,8 +7762,12 @@ def stairs(self, values, edges=None, *,
         if edges is None:
             edges = np.arange(len(values) + 1)
 
-        edges, values, baseline = self._process_unit_info(
-            [("x", edges), ("y", values), ("y", baseline)], kwargs)
+        if orientation == "vertical":
+            edges, values, baseline = self._process_unit_info(
+                [("x", edges), ("y", values), ("y", baseline)], kwargs)
+        else:
+            edges, values, baseline = self._process_unit_info(
+                [("y", edges), ("x", values), ("x", baseline)], kwargs)
 
         patch = mpatches.StepPatch(values,
                                    edges,