diff --git a/encode_test.go b/encode_test.go
index 725d9ba..112fb30 100644
--- a/encode_test.go
+++ b/encode_test.go
@@ -175,7 +175,7 @@ func TestEncoder_Encode(t *testing.T) {
 				{Extras: 8.0, Sampler: Index(2), Target: ChannelTarget{Extras: 8.0, Node: Index(5), Path: TRSTranslation}},
 			}},
 			{Extras: 8.0, Name: "an_3", Samplers: []*AnimationSampler{
-				{Extras: 8.0, Input: Index(1), Output: Index(1), Interpolation: InterpolationCubicSpline},
+				{Extras: 8.0, Input: 1, Output: 1, Interpolation: InterpolationCubicSpline},
 			}},
 		}}}, false},
 		{"withBufView", args{&Document{BufferViews: []*BufferView{
diff --git a/gltf.go b/gltf.go
index 049dd29..fc3ee17 100644
--- a/gltf.go
+++ b/gltf.go
@@ -426,9 +426,9 @@ type Animation struct {
 type AnimationSampler struct {
 	Extensions    Extensions    `json:"extensions,omitempty"`
 	Extras        interface{}   `json:"extras,omitempty"`
-	Input         *uint32       `json:"input,omitempty"` // The index of an accessor containing keyframe input values.
+	Input         uint32        `json:"input"` // The index of an accessor containing keyframe input values.
 	Interpolation Interpolation `json:"interpolation,omitempty" validate:"lte=2"`
-	Output        *uint32       `json:"output,omitempty"` // The index of an accessor containing keyframe output values.
+	Output        uint32        `json:"output"` // The index of an accessor containing keyframe output values.
 }
 
 // The Channel targets an animation's sampler at a node's property.