diff --git a/chatcompletion.go b/chatcompletion.go
index 962b69d0..e6cc1bf0 100644
--- a/chatcompletion.go
+++ b/chatcompletion.go
@@ -2742,6 +2742,15 @@ func (u ChatCompletionToolChoiceOptionUnionParam) GetType() *string {
 	return nil
 }
 
+func init() {
+	apijson.RegisterUnion[ChatCompletionToolChoiceOptionUnionParam](
+		"type",
+		apijson.Discriminator[ChatCompletionAllowedToolChoiceParam]("allowed_tools"),
+		apijson.Discriminator[ChatCompletionNamedToolChoiceParam]("function"),
+		apijson.Discriminator[ChatCompletionNamedToolChoiceCustomParam]("custom"),
+	)
+}
+
 // `none` means the model will not call any tool and instead generates a message.
 // `auto` means the model can pick between generating a message or calling one or
 // more tools. `required` means the model must call one or more tools.
diff --git a/internal/apijson/union.go b/internal/apijson/union.go
index ce0b6f25..075f87d5 100644
--- a/internal/apijson/union.go
+++ b/internal/apijson/union.go
@@ -2,9 +2,10 @@ package apijson
 
 import (
 	"errors"
-	"github.com/openai/openai-go/v3/packages/param"
 	"reflect"
 
+	"github.com/openai/openai-go/v3/packages/param"
+
 	"github.com/tidwall/gjson"
 )
 
@@ -66,7 +67,11 @@ func (d *decoderBuilder) newStructUnionDecoder(t reflect.Type) decoderFunc {
 	for _, variant := range unionEntry.variants {
 		// For each union variant, find a matching decoder and save it
 		for _, decoder := range decoders {
-			if decoder.field.Type.Elem() == variant.Type {
+			fieldType := decoder.field.Type
+			if fieldType.Kind() == reflect.Ptr {
+				fieldType = fieldType.Elem()
+			}
+			if fieldType == variant.Type {
 				discriminatedDecoders = append(discriminatedDecoders, discriminatedDecoder{
 					decoder,
 					variant.DiscriminatorValue,