diff --git a/sherpa-onnx/java-api/src/com/k2fsa/sherpa/onnx/OfflineModelConfig.java b/sherpa-onnx/java-api/src/com/k2fsa/sherpa/onnx/OfflineModelConfig.java
index 0576b0db..9e23a3a7 100644
--- a/sherpa-onnx/java-api/src/com/k2fsa/sherpa/onnx/OfflineModelConfig.java
+++ b/sherpa-onnx/java-api/src/com/k2fsa/sherpa/onnx/OfflineModelConfig.java
@@ -160,12 +160,14 @@ public class OfflineModelConfig {
             return this;
         }
 
-        public void setModelingUnit(String modelingUnit) {
+        public Builder setModelingUnit(String modelingUnit) {
             this.modelingUnit = modelingUnit;
+            return this;
         }
 
-        public void setBpeVocab(String bpeVocab) {
+        public Builder setBpeVocab(String bpeVocab) {
             this.bpeVocab = bpeVocab;
+            return this;
         }
     }
 }
\ No newline at end of file