diff --git a/CHANGELOG-PRERELEASE.md b/CHANGELOG-PRERELEASE.md
index 04672194b..38aab250f 100644
--- a/CHANGELOG-PRERELEASE.md
+++ b/CHANGELOG-PRERELEASE.md
@@ -16,6 +16,7 @@ The format is based on [Keep a Changelog].
 ### Removed
 
 ### Fixed
+- Animation clip length can be changed `#647`
 
 ### Security
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8c6394b6a..543705683 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ The format is based on [Keep a Changelog].
 ### Removed
 
 ### Fixed
+- Animation clip length can be changed `#647`
 
 ### Security
 
diff --git a/Editor/Processors/ApplyObjectMapping.cs b/Editor/Processors/ApplyObjectMapping.cs
index 70bcf4d5f..d62d6e88a 100644
--- a/Editor/Processors/ApplyObjectMapping.cs
+++ b/Editor/Processors/ApplyObjectMapping.cs
@@ -161,6 +161,15 @@ private Object CustomClone(Object o)
                 var newClip = new AnimationClip();
                 newClip.name = "rebased " + clip.name;
 
+                // copy m_UseHighQualityCurve with SerializedObject since m_UseHighQualityCurve doesn't have public API
+                using (var serializedClip = new SerializedObject(clip))
+                using (var serializedNewClip = new SerializedObject(newClip))
+                {
+                    serializedNewClip.FindProperty("m_UseHighQualityCurve")
+                        .boolValue = serializedClip.FindProperty("m_UseHighQualityCurve").boolValue;
+                    serializedNewClip.ApplyModifiedPropertiesWithoutUndo();
+                }
+
                 foreach (var binding in AnimationUtility.GetCurveBindings(clip))
                 {
                     var newBinding = _mapping.MapBinding(binding);
@@ -179,6 +188,16 @@ private Object CustomClone(Object o)
                         AnimationUtility.GetObjectReferenceCurve(clip, binding));
                 }
 
+                // ReSharper disable once CompareOfFloatsByEqualityOperator
+                if (newClip.length != clip.length)
+                {
+                    // if newClip has less properties than original clip (especially for no properties), 
+                    // length of newClip can be changed which is bad.
+                    newClip.SetCurve(
+                        "$AvatarOptimizerClipLengthDummy$", typeof(GameObject), "m_IsActive",
+                        AnimationCurve.Constant(clip.length, clip.length, 1f));
+                }
+
                 newClip.wrapMode = clip.wrapMode;
                 newClip.legacy = clip.legacy;
                 newClip.frameRate = clip.frameRate;