diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 3dfd5502778b..4e9457320c80 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -2949,6 +2949,8 @@ def errorbar(self, x, y, yerr=None, xerr=None,
                 upper errors.
             - *None*: No errorbar.
 
+            Note that all error arrays should have *positive* values.
+
             See :doc:`/gallery/statistics/errorbar_features`
             for an example on the usage of ``xerr`` and ``yerr``.