diff --git a/src/main/java/org/codelibs/fess/es/config/exentity/ElevateWord.java b/src/main/java/org/codelibs/fess/es/config/exentity/ElevateWord.java
index c80b380f0..2ab04d950 100644
--- a/src/main/java/org/codelibs/fess/es/config/exentity/ElevateWord.java
+++ b/src/main/java/org/codelibs/fess/es/config/exentity/ElevateWord.java
@@ -37,7 +37,7 @@ public class ElevateWord extends BsElevateWord {
 
     private String[] labelTypeIds;
 
-    private List<LabelType> labelTypeList;
+    private volatile List<LabelType> labelTypeList;
 
     /* (non-Javadoc)
      * @see org.codelibs.fess.db.exentity.CrawlingConfig#getLabelTypeIds()
diff --git a/src/main/java/org/codelibs/fess/es/config/exentity/LabelType.java b/src/main/java/org/codelibs/fess/es/config/exentity/LabelType.java
index e25b01b61..5b2101858 100644
--- a/src/main/java/org/codelibs/fess/es/config/exentity/LabelType.java
+++ b/src/main/java/org/codelibs/fess/es/config/exentity/LabelType.java
@@ -36,7 +36,7 @@ public class LabelType extends BsLabelType {
     private static final long serialVersionUID = 1L;
     private String[] roleTypeIds;
 
-    private List<RoleType> roleTypeList;
+    private volatile List<RoleType> roleTypeList;
 
     public String[] getRoleTypeIds() {
         if (roleTypeIds == null) {