diff --git a/CHANGELOG.md b/CHANGELOG.md
index 93b4126dd..c8064e331 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -53,6 +53,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed rotate FX not being applied to mask images [\#1399](https://github.com/Zulko/moviepy/pull/1399)
 - 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)
 
 
 ## [v2.0.0.dev2](https://github.com/zulko/moviepy/tree/v2.0.0.dev2) (2020-10-05)
diff --git a/moviepy/audio/fx/audio_fadein.py b/moviepy/audio/fx/audio_fadein.py
index a0158cff5..e62c6412e 100644
--- a/moviepy/audio/fx/audio_fadein.py
+++ b/moviepy/audio/fx/audio_fadein.py
@@ -1,23 +1,45 @@
 import numpy as np
 
-from moviepy.decorators import audio_video_fx
+from moviepy.decorators import audio_video_fx, convert_parameter_to_seconds
+
+
+def _mono_factor_getter():
+    return lambda t, duration: np.minimum(t / duration, 1)
+
+
+def _stereo_factor_getter(nchannels):
+    def getter(t, duration):
+        factor = np.minimum(t / duration, 1)
+        return np.array([factor for _ in range(nchannels)]).T
+
+    return getter
 
 
 @audio_video_fx
+@convert_parameter_to_seconds(["duration"])
 def audio_fadein(clip, duration):
     """Return an audio (or video) clip that is first mute, then the
     sound arrives progressively over ``duration`` seconds.
-    """
 
-    def fading(get_frame, t):
-        frame = get_frame(t)
+    Parameters
+    ----------
+
+    duration : float
+      How long does it take for the sound to return to its normal level.
 
-        if np.isscalar(t):
-            factor = min(1.0 * t / duration, 1)
-            factor = np.array([factor, factor])
-        else:
-            factor = np.minimum(1.0 * t / duration, 1)
-            factor = np.vstack([factor, factor]).T
-        return factor * frame
+    Examples
+    --------
+
+    >>> clip = VideoFileClip("media/chaplin.mp4")
+    >>> clip.fx(audio_fadein, "00:00:06")
+    """
+    get_factor = (
+        _mono_factor_getter()
+        if clip.nchannels == 1
+        else _stereo_factor_getter(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 c06823692..3de4f55d3 100644
--- a/tests/test_fx.py
+++ b/tests/test_fx.py
@@ -19,10 +19,12 @@
 )
 from moviepy.audio.fx import (
     audio_delay,
+    audio_fadein,
     audio_normalize,
     multiply_stereo_volume,
     multiply_volume,
 )
+from moviepy.tools import convert_to_seconds
 from moviepy.utils import close_all_clips
 from moviepy.video.fx import (
     blackwhite,
@@ -1279,5 +1281,66 @@ def test_audio_delay(duration, offset, n_repeats, decay):
         )
 
 
+@pytest.mark.parametrize("sound_type", ("stereo", "mono"))
+@pytest.mark.parametrize("fps", (44100, 22050))
+@pytest.mark.parametrize(
+    ("clip_duration", "fadein_duration"),
+    (
+        (
+            (0.2, 0.1),
+            (1, "00:00:00,4"),
+            (0.3, 0.13),
+        )
+    ),
+)
+def test_audio_fadein(sound_type, fps, clip_duration, fadein_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_fadein(clip, fadein_duration)
+
+    # first frame is muted
+    first_frame = new_clip.get_frame(0)
+    if sound_type == "stereo":
+        assert len(first_frame) > 1
+        for value in first_frame:
+            assert value == 0.0
+    else:
+        assert first_frame == 0.0
+
+    fadein_duration = convert_to_seconds(fadein_duration)
+
+    n_parts = 10
+
+    # cut transformed part into subclips and check the expected max_volume for
+    # each one
+    time_foreach_part = fadein_duration / n_parts
+    start_times = np.arange(0, fadein_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 = (i + 1) / n_parts
+        assert round(subclip_max_volume, 2) in [
+            possible_value,
+            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 - fadein_duration) / n_parts
+    start_times = np.arange(fadein_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()
+
+        assert round(subclip_max_volume, 4) == 1
+
+
 if __name__ == "__main__":
     pytest.main()