diff --git a/doc/api/next_api_changes/deprecations/20686-AL.rst b/doc/api/next_api_changes/deprecations/20686-AL.rst
new file mode 100644
index 000000000000..929d3eaeaa6f
--- /dev/null
+++ b/doc/api/next_api_changes/deprecations/20686-AL.rst
@@ -0,0 +1,2 @@
+All parameters of ``imshow`` starting from *aspect* will become keyword-only
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/lib/matplotlib/_api/deprecation.py b/lib/matplotlib/_api/deprecation.py
index 4b8f50f188ee..ae14f29fea5d 100644
--- a/lib/matplotlib/_api/deprecation.py
+++ b/lib/matplotlib/_api/deprecation.py
@@ -249,6 +249,14 @@ def __set_name__(self, owner, name):
             name=name))
 
 
+# Used by _copy_docstring_and_deprecators to redecorate pyplot wrappers and
+# boilerplate.py to retrieve original signatures.  It may seem natural to store
+# this information as an attribute on the wrapper, but if the wrapper gets
+# itself functools.wraps()ed, then such attributes are silently propagated to
+# the outer wrapper, which is not desired.
+DECORATORS = {}
+
+
 def rename_parameter(since, old, new, func=None):
     """
     Decorator indicating that parameter *old* of *func* is renamed to *new*.
@@ -268,8 +276,10 @@ def rename_parameter(since, old, new, func=None):
         def func(good_name): ...
     """
 
+    decorator = functools.partial(rename_parameter, since, old, new)
+
     if func is None:
-        return functools.partial(rename_parameter, since, old, new)
+        return decorator
 
     signature = inspect.signature(func)
     assert old not in signature.parameters, (
@@ -294,6 +304,7 @@ def wrapper(*args, **kwargs):
     # would both show up in the pyplot function for an Axes method as well and
     # pyplot would explicitly pass both arguments to the Axes method.
 
+    DECORATORS[wrapper] = decorator
     return wrapper
 
 
@@ -330,8 +341,10 @@ def delete_parameter(since, name, func=None, **kwargs):
         def func(used_arg, other_arg, unused, more_args): ...
     """
 
+    decorator = functools.partial(delete_parameter, since, name, **kwargs)
+
     if func is None:
-        return functools.partial(delete_parameter, since, name, **kwargs)
+        return decorator
 
     signature = inspect.signature(func)
     # Name of `**kwargs` parameter of the decorated function, typically
@@ -399,6 +412,7 @@ def wrapper(*inner_args, **inner_kwargs):
                 **kwargs)
         return func(*inner_args, **inner_kwargs)
 
+    DECORATORS[wrapper] = decorator
     return wrapper
 
 
@@ -406,10 +420,16 @@ def make_keyword_only(since, name, func=None):
     """
     Decorator indicating that passing parameter *name* (or any of the following
     ones) positionally to *func* is being deprecated.
+
+    When used on a method that has a pyplot wrapper, this should be the
+    outermost decorator, so that :file:`boilerplate.py` can access the original
+    signature.
     """
 
+    decorator = functools.partial(make_keyword_only, since, name)
+
     if func is None:
-        return functools.partial(make_keyword_only, since, name)
+        return decorator
 
     signature = inspect.signature(func)
     POK = inspect.Parameter.POSITIONAL_OR_KEYWORD
@@ -419,19 +439,16 @@ def make_keyword_only(since, name, func=None):
         f"Matplotlib internal error: {name!r} must be a positional-or-keyword "
         f"parameter for {func.__name__}()")
     names = [*signature.parameters]
-    kwonly = [name for name in names[names.index(name):]
+    name_idx = names.index(name)
+    kwonly = [name for name in names[name_idx:]
               if signature.parameters[name].kind == POK]
-    func.__signature__ = signature.replace(parameters=[
-        param.replace(kind=KWO) if param.name in kwonly else param
-        for param in signature.parameters.values()])
 
     @functools.wraps(func)
     def wrapper(*args, **kwargs):
         # Don't use signature.bind here, as it would fail when stacked with
         # rename_parameter and an "old" argument name is passed in
         # (signature.bind would fail, but the actual call would succeed).
-        idx = [*func.__signature__.parameters].index(name)
-        if len(args) > idx:
+        if len(args) > name_idx:
             warn_deprecated(
                 since, message="Passing the %(name)s %(obj_type)s "
                 "positionally is deprecated since Matplotlib %(since)s; the "
@@ -439,6 +456,11 @@ def wrapper(*args, **kwargs):
                 name=name, obj_type=f"parameter of {func.__name__}()")
         return func(*args, **kwargs)
 
+    # Don't modify *func*'s signature, as boilerplate.py needs it.
+    wrapper.__signature__ = signature.replace(parameters=[
+        param.replace(kind=KWO) if param.name in kwonly else param
+        for param in signature.parameters.values()])
+    DECORATORS[wrapper] = decorator
     return wrapper
 
 
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 92a6d319ab3c..a52ed419c0ff 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -5285,6 +5285,7 @@ def fill_betweenx(self, y, x1, x2=0, where=None,
         replace_names=["y", "x1", "x2", "where"])
 
     #### plotting z(x, y): imshow, pcolor and relatives, contour
+    @_api.make_keyword_only("3.5", "aspect")
     @_preprocess_data()
     def imshow(self, X, cmap=None, norm=None, aspect=None,
                interpolation=None, alpha=None, vmin=None, vmax=None,
diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
index 6e56cd4f4d8e..7c29cb1b7ba1 100644
--- a/lib/matplotlib/pyplot.py
+++ b/lib/matplotlib/pyplot.py
@@ -72,14 +72,6 @@
 _log = logging.getLogger(__name__)
 
 
-_code_objs = {
-    _api.rename_parameter:
-        _api.rename_parameter("", "old", "new", lambda new: None).__code__,
-    _api.make_keyword_only:
-        _api.make_keyword_only("", "p", lambda p: None).__code__,
-}
-
-
 def _copy_docstring_and_deprecators(method, func=None):
     if func is None:
         return functools.partial(_copy_docstring_and_deprecators, method)
@@ -88,14 +80,9 @@ def _copy_docstring_and_deprecators(method, func=None):
     # or @_api.make_keyword_only decorators; if so, propagate them to the
     # pyplot wrapper as well.
     while getattr(method, "__wrapped__", None) is not None:
-        for decorator_maker, code in _code_objs.items():
-            if method.__code__ is code:
-                kwargs = {
-                    k: v.cell_contents
-                    for k, v in zip(code.co_freevars, method.__closure__)}
-                assert kwargs["func"] is method.__wrapped__
-                kwargs.pop("func")
-                decorators.append(decorator_maker(**kwargs))
+        decorator = _api.deprecation.DECORATORS.get(method)
+        if decorator:
+            decorators.append(decorator)
         method = method.__wrapped__
     for decorator in decorators[::-1]:
         func = decorator(func)
diff --git a/tools/boilerplate.py b/tools/boilerplate.py
index 214cd408a344..46c8d3656373 100644
--- a/tools/boilerplate.py
+++ b/tools/boilerplate.py
@@ -138,7 +138,13 @@ def generate_function(name, called_fullname, template, **kwargs):
     class_name, called_name = called_fullname.split('.')
     class_ = {'Axes': Axes, 'Figure': Figure}[class_name]
 
-    signature = inspect.signature(getattr(class_, called_name))
+    meth = getattr(class_, called_name)
+    decorator = _api.deprecation.DECORATORS.get(meth)
+    # Generate the wrapper with the non-kwonly signature, as it will get
+    # redecorated with make_keyword_only by _copy_docstring_and_deprecators.
+    if decorator and decorator.func is _api.make_keyword_only:
+        meth = meth.__wrapped__
+    signature = inspect.signature(meth)
     # Replace self argument.
     params = list(signature.parameters.values())[1:]
     signature = str(signature.replace(parameters=[