diff --git a/CHANGELOG.md b/CHANGELOG.md
index c8064e331..e4a3c77bb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -54,6 +54,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed opacity error blitting VideoClips [\#1552](https://github.com/Zulko/moviepy/pull/1552)
 - Fixed rotation metadata of input not being taken into account rendering VideoClips [\#577](https://github.com/Zulko/moviepy/pull/577)
 - Fixed mono clips crashing when `audio_fadein` FX applied [\#1574](https://github.com/Zulko/moviepy/pull/1574)
+- Fixed mono clips crashing when `audio_fadeout` FX applied [\#1578](https://github.com/Zulko/moviepy/pull/1578)
 
 
 ## [v2.0.0.dev2](https://github.com/zulko/moviepy/tree/v2.0.0.dev2) (2020-10-05)
diff --git a/moviepy/audio/fx/audio_fadeout.py b/moviepy/audio/fx/audio_fadeout.py
index a5b693be0..c7a1316ca 100644
--- a/moviepy/audio/fx/audio_fadeout.py
+++ b/moviepy/audio/fx/audio_fadeout.py
@@ -1,24 +1,51 @@
 import numpy as np
 
-from moviepy.decorators import audio_video_fx, requires_duration
+from moviepy.decorators import (
+    audio_video_fx,
+    convert_parameter_to_seconds,
+    requires_duration,
+)
+
+
+def _mono_factor_getter(clip_duration):
+    return lambda t, duration: np.minimum(1.0 * (clip_duration - t) / duration, 1)
+
+
+def _stereo_factor_getter(clip_duration, nchannels):
+    def getter(t, duration):
+        factor = np.minimum(1.0 * (clip_duration - t) / duration, 1)
+        return np.array([factor for _ in range(nchannels)]).T
+
+    return getter
 
 
 @audio_video_fx
 @requires_duration
+@convert_parameter_to_seconds(["duration"])
 def audio_fadeout(clip, duration):
     """Return a sound clip where the sound fades out progressively
     over ``duration`` seconds at the end of the clip.
-    """
 
-    def fading(get_frame, t):
-        frame = get_frame(t)
+    Parameters
+    ----------
+
+    duration : float
+      How long does it take for the sound to reach the zero level at the end
+      of the clip.
 
-        if np.isscalar(t):
-            factor = min(1.0 * (clip.duration - t) / duration, 1)
-            factor = np.array([factor, factor])
-        else:
-            factor = np.minimum(1.0 * (clip.duration - t) / duration, 1)
-            factor = np.vstack([factor, factor]).T
-        return factor * frame
+    Examples
+    --------
+
+    >>> clip = VideoFileClip("media/chaplin.mp4")
+    >>> clip.fx(audio_fadeout, "00:00:06")
+    """
+    get_factor = (
+        _mono_factor_getter(clip.duration)
+        if clip.nchannels == 1
+        else _stereo_factor_getter(clip.duration, clip.nchannels)
+    )
 
-    return clip.transform(fading, keep_duration=True)
+    return clip.transform(
+        lambda get_frame, t: get_factor(t, duration) * get_frame(t),
+        keep_duration=True,
+    )
diff --git a/tests/test_fx.py b/tests/test_fx.py
index 3de4f55d3..52bdb838a 100644
--- a/tests/test_fx.py
+++ b/tests/test_fx.py
@@ -20,6 +20,7 @@
 from moviepy.audio.fx import (
     audio_delay,
     audio_fadein,
+    audio_fadeout,
     audio_normalize,
     multiply_stereo_volume,
     multiply_volume,
@@ -1342,5 +1343,61 @@ def test_audio_fadein(sound_type, fps, clip_duration, fadein_duration):
         assert round(subclip_max_volume, 4) == 1
 
 
+@pytest.mark.parametrize("sound_type", ("stereo", "mono"))
+@pytest.mark.parametrize("fps", (44100, 22050))
+@pytest.mark.parametrize(
+    ("clip_duration", "fadeout_duration"),
+    (
+        (
+            (0.2, 0.1),
+            (0.7, "00:00:00,4"),
+            (0.3, 0.13),
+        )
+    ),
+)
+def test_audio_fadeout(sound_type, fps, clip_duration, fadeout_duration):
+    if sound_type == "stereo":
+        make_frame = lambda t: np.array(
+            [np.sin(440 * 2 * np.pi * t), np.sin(160 * 2 * np.pi * t)]
+        ).T.copy(order="C")
+    else:
+        make_frame = lambda t: np.sin(440 * 2 * np.pi * t)
+
+    clip = AudioClip(make_frame, duration=clip_duration, fps=fps)
+    new_clip = audio_fadeout(clip, fadeout_duration)
+
+    fadeout_duration = convert_to_seconds(fadeout_duration)
+
+    n_parts = 10
+
+    # cut transformed part into subclips and check the expected max_volume for
+    # each one
+    time_foreach_part = fadeout_duration / n_parts
+    start_times = np.arange(
+        clip_duration - fadeout_duration,
+        clip_duration,
+        time_foreach_part,
+    )
+    for i, start_time in enumerate(start_times):
+        end_time = start_time + time_foreach_part
+        subclip_max_volume = new_clip.subclip(start_time, end_time).max_volume()
+
+        possible_value = 1 - i * 0.1
+        assert round(subclip_max_volume, 2) in [
+            round(possible_value, 2),
+            round(possible_value - 0.01, 5),
+        ]
+
+    # cut non transformed part into subclips and check the expected max_volume
+    # for each one (almost 1)
+    time_foreach_part = (clip_duration - fadeout_duration) / n_parts
+    start_times = np.arange(0, clip_duration - fadeout_duration, time_foreach_part)
+    for i, start_time in enumerate(start_times):
+        end_time = start_time + time_foreach_part
+        subclip_max_volume = new_clip.subclip(start_time, end_time).max_volume()
+
+        assert round(subclip_max_volume, 4) == 1
+
+
 if __name__ == "__main__":
     pytest.main()