diff --git a/lib/matplotlib/sphinxext/plot_directive.py b/lib/matplotlib/sphinxext/plot_directive.py
index 6a9d316dfbf4..3136e6ea5631 100644
--- a/lib/matplotlib/sphinxext/plot_directive.py
+++ b/lib/matplotlib/sphinxext/plot_directive.py
@@ -197,7 +197,7 @@ def _option_format(arg):
 
 
 def _deprecated_option_encoding(arg):
-    _api.warn_deprecated("3.5", "encoding", obj_type="option")
+    _api.warn_deprecated("3.5", name="encoding", obj_type="option")
     return directives.encoding(arg)
 
 
diff --git a/lib/matplotlib/tests/tinypages/some_plots.rst b/lib/matplotlib/tests/tinypages/some_plots.rst
index bab58fd3a8c2..fdf7db93bc7c 100644
--- a/lib/matplotlib/tests/tinypages/some_plots.rst
+++ b/lib/matplotlib/tests/tinypages/some_plots.rst
@@ -120,9 +120,11 @@ Plot 14 uses ``include-source``:
 
     # Only a comment
 
-Plot 15 uses an external file with the plot commands and a caption:
+Plot 15 uses an external file with the plot commands and a caption (the
+encoding is ignored and just verifies the deprecation is not broken):
 
 .. plot:: range4.py
+   :encoding: utf-8
 
    This is the caption for plot 15.