diff --git a/CHANGES.rst b/CHANGES.rst
index 5328c2c..93144b3 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,6 +1,13 @@
 Latest changes
 ==============
 
+Development version
+-------------------
+
+- Fix joblib.Memory bug with the ``ignore`` parameter when the cached function
+  is a decorated function.
+  https://github.com/joblib/joblib/pull/1165
+
 1.0.1
 -----
 
diff --git a/joblib/func_inspect.py b/joblib/func_inspect.py
index ec6bb4a..3751347 100644
--- a/joblib/func_inspect.py
+++ b/joblib/func_inspect.py
@@ -171,10 +171,9 @@ def get_func_name(func, resolv_alias=True, win_characters=True):
     return module, name
 
 
-def _signature_str(function_name, arg_spec):
+def _signature_str(function_name, arg_sig):
     """Helper function to output a function signature"""
-    arg_spec_str = inspect.formatargspec(*arg_spec)
-    return '{}{}'.format(function_name, arg_spec_str)
+    return '{}{}'.format(function_name, arg_sig)
 
 
 def _function_called_str(function_name, args, kwargs):
@@ -221,20 +220,34 @@ def filter_args(func, ignore_lst, args=(), kwargs=dict()):
             warnings.warn('Cannot inspect object %s, ignore list will '
                           'not work.' % func, stacklevel=2)
         return {'*': args, '**': kwargs}
-    arg_spec = inspect.getfullargspec(func)
-    arg_names = arg_spec.args + arg_spec.kwonlyargs
-    arg_defaults = arg_spec.defaults or ()
-    if arg_spec.kwonlydefaults:
-        arg_defaults = arg_defaults + tuple(arg_spec.kwonlydefaults[k]
-                                            for k in arg_spec.kwonlyargs
-                                            if k in arg_spec.kwonlydefaults)
-    arg_varargs = arg_spec.varargs
-    arg_varkw = arg_spec.varkw
-
+    arg_sig = inspect.signature(func)
+    arg_names = []
+    arg_defaults = []
+    arg_kwonlyargs = []
+    arg_varargs = None
+    arg_varkw = None
+    for param in arg_sig.parameters.values():
+        if param.kind is param.POSITIONAL_OR_KEYWORD:
+            arg_names.append(param.name)
+        elif param.kind is param.KEYWORD_ONLY:
+            arg_names.append(param.name)
+            arg_kwonlyargs.append(param.name)
+        elif param.kind is param.VAR_POSITIONAL:
+            arg_varargs = param.name
+        elif param.kind is param.VAR_KEYWORD:
+            arg_varkw = param.name
+        if param.default is not param.empty:
+            arg_defaults.append(param.default)
     if inspect.ismethod(func):
         # First argument is 'self', it has been removed by Python
         # we need to add it back:
         args = [func.__self__, ] + args
+        # func is an instance method, inspect.signature(func) does not
+        # include self, we need to fetch it from the class method, i.e
+        # func.__func__
+        class_method_sig = inspect.signature(func.__func__)
+        self_name = next(iter(class_method_sig.parameters))
+        arg_names = [self_name] + arg_names
     # XXX: Maybe I need an inspect.isbuiltin to detect C-level methods, such
     # as on ndarrays.
 
@@ -244,7 +257,7 @@ def filter_args(func, ignore_lst, args=(), kwargs=dict()):
     for arg_position, arg_name in enumerate(arg_names):
         if arg_position < len(args):
             # Positional argument or keyword argument given as positional
-            if arg_name not in arg_spec.kwonlyargs:
+            if arg_name not in arg_kwonlyargs:
                 arg_dict[arg_name] = args[arg_position]
             else:
                 raise ValueError(
@@ -252,7 +265,7 @@ def filter_args(func, ignore_lst, args=(), kwargs=dict()):
                     'positional parameter for %s:\n'
                     '     %s was called.'
                     % (arg_name,
-                       _signature_str(name, arg_spec),
+                       _signature_str(name, arg_sig),
                        _function_called_str(name, args, kwargs))
                 )
 
@@ -268,7 +281,7 @@ def filter_args(func, ignore_lst, args=(), kwargs=dict()):
                     raise ValueError(
                         'Wrong number of arguments for %s:\n'
                         '     %s was called.'
-                        % (_signature_str(name, arg_spec),
+                        % (_signature_str(name, arg_sig),
                            _function_called_str(name, args, kwargs))
                     ) from e
 
@@ -296,7 +309,7 @@ def filter_args(func, ignore_lst, args=(), kwargs=dict()):
             raise ValueError("Ignore list: argument '%s' is not defined for "
                              "function %s"
                              % (item,
-                                _signature_str(name, arg_spec))
+                                _signature_str(name, arg_sig))
                              )
     # XXX: Return a sorted list of pairs?
     return arg_dict
diff --git a/joblib/memory.py b/joblib/memory.py
index 424d9fe..f5d59eb 100644
--- a/joblib/memory.py
+++ b/joblib/memory.py
@@ -882,7 +882,10 @@ class Memory(Logger):
             as functions are evaluated.
 
         bytes_limit: int, optional
-            Limit in bytes of the size of the cache.
+            Limit in bytes of the size of the cache. By default, the size of
+            the cache is unlimited.
+            Note: You need to call :meth:`joblib.Memory.reduce_size` to
+            actually reduce the cache size to be less than ``bytes_limit``.
 
         backend_options: dict, optional
             Contains a dictionnary of named parameters used to configure

diff --git a/joblib/test/test_memory.py b/joblib/test/test_memory.py
index ad0ddf4..e917871 100644
--- a/joblib/test/test_memory.py
+++ b/joblib/test/test_memory.py
@@ -6,6 +6,7 @@ Test the memory module.
 # Copyright (c) 2009 Gael Varoquaux
 # License: BSD Style, 3 clauses.
 
+import functools
 import gc
 import shutil
 import os
@@ -488,6 +489,32 @@ def test_memory_ignore(tmpdir):
     assert len(accumulator) == 1
 
 
+def test_memory_ignore_decorated(tmpdir):
+    " Test the ignore feature of memory on a decorated function "
+    memory = Memory(location=tmpdir.strpath, verbose=0)
+    accumulator = list()
+
+    def decorate(f):
+        @functools.wraps(f)
+        def wrapped(*args, **kwargs):
+            return f(*args, **kwargs)
+        return wrapped
+
+    @memory.cache(ignore=['y'])
+    @decorate
+    def z(x, y=1):
+        accumulator.append(1)
+
+    assert z.ignore == ['y']
+
+    z(0, y=1)
+    assert len(accumulator) == 1
+    z(0, y=1)
+    assert len(accumulator) == 1
+    z(0, y=2)
+    assert len(accumulator) == 1
+
+
 def test_memory_args_as_kwargs(tmpdir):
     """Non-regression test against 0.12.0 changes.
 

Use inspect.signature() instead of inspect.getfullargspec()
Currently, the implementation of `Memory.cache()` implements the `ignore` option using [`inspect.getfullargspec()`](https://docs.python.org/3/library/inspect.html#inspect.getfullargspec).  However, this function does not handle decorated functions correctly; [`inspect.signature()`](https://docs.python.org/3/library/inspect.html#inspect.signature), on the other hand, does.  Observe:

```python
from functools import wraps
import inspect

def decorate(f):
    @wraps(f)
    def wrapped(*args, **kwargs):
        return f(*args, **kwargs)
    return wrapped

@decorate
def foo(arg, extra=None):
    return arg

print(inspect.signature(foo))
print(inspect.getfullargspec(foo))
```

This prints out:

```
(arg, extra=None)
FullArgSpec(args=[], varargs='args', varkw='kwargs', defaults=None, kwonlyargs=[], kwonlydefaults=None, annotations={})
```

Note that `signature()` reports the signature of the original `foo`, while `getfullargspec()` reports the signature of `wrapped`.

As a consequence of this, using the `ignore` option on a Memory-cached function with an intervening decorator does not work.  Example:

```python
from functools import wraps
import inspect
from joblib import Memory

mem = Memory("cache", verbose=0)

def decorate(f):
    @wraps(f)
    def wrapped(*args, **kwargs):
        return f(*args, **kwargs)
    return wrapped

@mem.cache(ignore=["extra"])
@decorate
def foo(arg, extra=None):
    return arg

foo(1)
```

This fails with the error `ValueError: Ignore list: argument 'extra' is not defined for function foo(*args, **kwargs)`.
joblib/test/test_memory.py::test_memory_ignore_decorated
joblib/test/test_memory.py::test_memory_integration joblib/test/test_memory.py::test_no_memory joblib/test/test_memory.py::test_memory_kwarg joblib/test/test_memory.py::test_memory_lambda joblib/test/test_memory.py::test_memory_name_collision joblib/test/test_memory.py::test_memory_warning_lambda_collisions joblib/test/test_memory.py::test_memory_warning_collision_detection joblib/test/test_memory.py::test_memory_partial joblib/test/test_memory.py::test_memory_eval joblib/test/test_memory.py::test_argument_change joblib/test/test_memory.py::test_memory_exception joblib/test/test_memory.py::test_memory_ignore joblib/test/test_memory.py::test_memory_args_as_kwargs joblib/test/test_memory.py::test_partial_decoration[ignore0-100-r] joblib/test/test_memory.py::test_partial_decoration[ignore1-10-None] joblib/test/test_memory.py::test_func_dir joblib/test/test_memory.py::test_persistence joblib/test/test_memory.py::test_call_and_shelve joblib/test/test_memory.py::test_call_and_shelve_argument_hash joblib/test/test_memory.py::test_call_and_shelve_lazily_load_stored_result joblib/test/test_memory.py::test_memorized_pickling joblib/test/test_memory.py::test_memorized_repr joblib/test/test_memory.py::test_memory_file_modification joblib/test/test_memory.py::test_memory_in_memory_function_code_change joblib/test/test_memory.py::test_clear_memory_with_none_location joblib/test/test_memory.py::test_memory_func_with_kwonly_args joblib/test/test_memory.py::test_memory_func_with_signature joblib/test/test_memory.py::test__get_items joblib/test/test_memory.py::test__get_items_to_delete joblib/test/test_memory.py::test_memory_reduce_size joblib/test/test_memory.py::test_memory_clear joblib/test/test_memory.py::test_cached_function_race_condition_when_persisting_output joblib/test/test_memory.py::test_cached_function_race_condition_when_persisting_output_2 joblib/test/test_memory.py::test_memory_recomputes_after_an_error_while_loading_results joblib/test/test_memory.py::test_register_invalid_store_backends_key[None] joblib/test/test_memory.py::test_register_invalid_store_backends_key[invalid_prefix1] joblib/test/test_memory.py::test_register_invalid_store_backends_key[invalid_prefix2] joblib/test/test_memory.py::test_register_invalid_store_backends_object joblib/test/test_memory.py::test_memory_default_store_backend joblib/test/test_memory.py::test_warning_on_unknown_location_type joblib/test/test_memory.py::test_instanciate_incomplete_store_backend joblib/test/test_memory.py::test_dummy_store_backend joblib/test/test_memory.py::test_instanciate_store_backend_with_pathlib_path joblib/test/test_memory.py::test_filesystem_store_backend_repr joblib/test/test_memory.py::test_memory_objects_repr joblib/test/test_memory.py::test_memorized_result_pickle joblib/test/test_memory.py::test_memory_pickle_dump_load[memory_kwargs0] joblib/test/test_memory.py::test_memory_pickle_dump_load[memory_kwargs1]