diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBinary.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBinary.java
index 775e33841..e52a16c36 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBinary.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBinary.java
@@ -418,8 +418,9 @@ public class SkeletonBinary extends SkeletonLoader {
 				case CONSTRAINT_SLIDER -> {
 					var data = new SliderData(name);
 					data.skinRequired = (nn & 1) != 0;
-					if ((nn & 2) != 0) data.setup.mix = (nn & 4) != 0 ? input.readFloat() : 1;
-					if ((nn & 8) != 0) data.setup.time = input.readFloat();
+					data.additive = (nn & 2) != 0;
+					if ((nn & 4) != 0) data.setup.mix = (nn & 8) != 0 ? input.readFloat() : 1;
+					if ((nn & 16) != 0) data.setup.time = input.readFloat();
 					constraints[i] = data;
 				}
 				}
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonJson.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonJson.java
index cfeb6e9c5..dc6c84375 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonJson.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonJson.java
@@ -408,6 +408,7 @@ public class SkeletonJson extends SkeletonLoader {
 			case "slider" -> {
 				var data = new SliderData(name);
 				data.skinRequired = skinRequired;
+				data.additive = constraintMap.getBoolean("additive", false);
 				data.setup.time = constraintMap.getFloat("time", 0);
 				data.setup.mix = constraintMap.getFloat("mix", 1);
 				skeletonData.constraints.add(data);
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Slider.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Slider.java
index c8814cba6..88f461ce5 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Slider.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Slider.java
@@ -71,7 +71,8 @@ public class Slider extends Constraint<Slider, SliderData, SliderPose> {
 		}
 
 		SliderPose pose = applied;
-		data.animation.apply(skeleton, pose.time, pose.time, false, null, pose.mix, MixBlend.replace, MixDirection.in, true);
+		data.animation.apply(skeleton, pose.time, pose.time, false, null, pose.mix, data.additive ? MixBlend.add : MixBlend.replace,
+			MixDirection.in, true);
 	}
 
 	void sort (Skeleton skeleton) {
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SliderData.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SliderData.java
index 55fbc47dc..9ce8c9bd8 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SliderData.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SliderData.java
@@ -34,6 +34,7 @@ package com.esotericsoftware.spine;
  * See <a href="https://esotericsoftware.com/spine-physics-constraints">Physics constraints</a> in the Spine User Guide. */
 public class SliderData extends ConstraintData<Slider, SliderPose> {
 	Animation animation;
+	boolean additive;
 
 	public SliderData (String name) {
 		super(name, new SliderPose());
@@ -50,4 +51,12 @@ public class SliderData extends ConstraintData<Slider, SliderPose> {
 	public void setAnimation (Animation animation) {
 		this.animation = animation;
 	}
+
+	public boolean getAdditive () {
+		return additive;
+	}
+
+	public void setAdditive (boolean additive) {
+		this.additive = additive;
+	}
 }