diff --git a/Assets/UniGLTF/Runtime/SpringBoneJobs/Blittables/BlittableSpan.cs b/Assets/UniGLTF/Runtime/SpringBoneJobs/Blittables/BlittableSpan.cs
index 425d2a6be..bf7a400ef 100644
--- a/Assets/UniGLTF/Runtime/SpringBoneJobs/Blittables/BlittableSpan.cs
+++ b/Assets/UniGLTF/Runtime/SpringBoneJobs/Blittables/BlittableSpan.cs
@@ -3,11 +3,20 @@ using System;
 namespace UniGLTF.SpringBoneJobs.Blittables
 {
     [Serializable]
-    public struct BlittableSpan
+    public readonly struct BlittableSpan
     {
-        public int startIndex;
-        public int count;
+        private readonly int _startIndex;
+        private readonly int _count;
+        
+        public int startIndex => _startIndex;
+        public int count => _count;
 
         public int EndIndex => startIndex + count;
+
+        public BlittableSpan(int startIndex, int count)
+        {
+            _startIndex = startIndex;
+            _count = count;
+        }
     }
 }
\ No newline at end of file
diff --git a/Assets/UniGLTF/Runtime/SpringBoneJobs/FastSpringBoneConbinedBuffer.cs b/Assets/UniGLTF/Runtime/SpringBoneJobs/FastSpringBoneConbinedBuffer.cs
index 8e8cc7835..fb65bc910 100644
--- a/Assets/UniGLTF/Runtime/SpringBoneJobs/FastSpringBoneConbinedBuffer.cs
+++ b/Assets/UniGLTF/Runtime/SpringBoneJobs/FastSpringBoneConbinedBuffer.cs
@@ -249,8 +249,8 @@ namespace UniGLTF.SpringBoneJobs
             {
                 var spring = SrcSprings[index];
                 spring.modelIndex = ModelIndex;
-                spring.colliderSpan.startIndex += CollidersOffset;
-                spring.logicSpan.startIndex += LogicsOffset;
+                spring.colliderSpan = new BlittableSpan(spring.colliderSpan.startIndex + CollidersOffset, spring.colliderSpan.count);
+                spring.logicSpan = new BlittableSpan(spring.logicSpan.startIndex + LogicsOffset, spring.logicSpan.count);
                 spring.transformIndexOffset = TransformOffset;
                 DestSprings[index] = spring;
             }
diff --git a/Assets/UniGLTF/Runtime/SpringBoneJobs/InputPorts/FastSpringBoneBuffer.cs b/Assets/UniGLTF/Runtime/SpringBoneJobs/InputPorts/FastSpringBoneBuffer.cs
index a87346731..3c0fddec4 100644
--- a/Assets/UniGLTF/Runtime/SpringBoneJobs/InputPorts/FastSpringBoneBuffer.cs
+++ b/Assets/UniGLTF/Runtime/SpringBoneJobs/InputPorts/FastSpringBoneBuffer.cs
@@ -69,16 +69,8 @@ namespace UniGLTF.SpringBoneJobs.InputPorts
             {
                 var blittableSpring = new BlittableSpring
                 {
-                    colliderSpan = new BlittableSpan
-                    {
-                        startIndex = blittableColliders.Count,
-                        count = spring.colliders.Length,
-                    },
-                    logicSpan = new BlittableSpan
-                    {
-                        startIndex = blittableJoints.Count,
-                        count = spring.joints.Length - 1,
-                    },
+                    colliderSpan = new BlittableSpan(blittableColliders.Count,spring.colliders.Length),
+                    logicSpan = new BlittableSpan(blittableJoints.Count, spring.joints.Length - 1),
                     centerTransformIndex = Array.IndexOf(Transforms, spring.center),
                 };
                 blittableSprings.Add(blittableSpring);