diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1a2a26a11..2bcdb40cc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,6 +34,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improve perfs of decorator by pre-computing arguments
 - Fix textclip being cut or of impredictable height (see issues #2325, #2260 and #2268)
 - Fix TimeMirror and TimeSymmetrize cutting last second of clip
+- ImageSequenceClip was wrong when calculating fps with duration and no fps (see issue #2351)
 - Fix audiopreview not working with ffplay >= 7.0.0
 
 ## [v2.1.2](https://github.com/zulko/moviepy/tree/master)
diff --git a/moviepy/video/io/ImageSequenceClip.py b/moviepy/video/io/ImageSequenceClip.py
index 96b407f0c..f1e6588c5 100644
--- a/moviepy/video/io/ImageSequenceClip.py
+++ b/moviepy/video/io/ImageSequenceClip.py
@@ -110,7 +110,7 @@ def __init__(
         self.sequence = sequence
 
         if fps is None:
-            self.fps = self.duration / len(sequence)
+            self.fps = len(sequence) / self.duration
 
         def find_image_index(t):
             return max(