diff --git a/spine-cpp/src/spine/Slider.cpp b/spine-cpp/src/spine/Slider.cpp
index 014ea2ec3..c996ce8c9 100644
--- a/spine-cpp/src/spine/Slider.cpp
+++ b/spine-cpp/src/spine/Slider.cpp
@@ -117,7 +117,8 @@ void Slider::sort(Skeleton &skeleton) {
 				skeleton.constrained((Posed &) *constraints[timeline->getConstraintIndex()]);
 		} else if (t->getRTTI().instanceOf(ConstraintTimeline::rtti)) {
 			ConstraintTimeline *timeline = (ConstraintTimeline *) t;
-			skeleton.constrained((Posed &) *constraints[timeline->getConstraintIndex()]);
+			int index = timeline->getConstraintIndex();
+			if (index != -1) skeleton.constrained((Posed &) *constraints[timeline->getConstraintIndex()]);
 		}
 	}
 }
diff --git a/spine-flutter/lib/assets/libspine_flutter.wasm b/spine-flutter/lib/assets/libspine_flutter.wasm
index 59e5c58e2..6e5839b44 100755
Binary files a/spine-flutter/lib/assets/libspine_flutter.wasm and b/spine-flutter/lib/assets/libspine_flutter.wasm differ