diff --git a/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/Borders.java b/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/Borders.java
index f2763f4fab..2ab27d37da 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/Borders.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/Borders.java
@@ -17,6 +17,7 @@
 
 package org.apache.poi.xwpf.usermodel;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -598,12 +599,14 @@ public enum Borders {
 
     ZIG_ZAG_STITCH(191);
 
-    private static Map<Integer, Borders> imap = new HashMap<>();
+    private static final Map<Integer, Borders> imap;
 
     static {
+        final Map<Integer, Borders> tempMap = new HashMap<>();
         for (Borders p : values()) {
-            imap.put(Integer.valueOf(p.getValue()), p);
+            tempMap.put(Integer.valueOf(p.getValue()), p);
         }
+        imap = Collections.unmodifiableMap(tempMap);
     }
 
     private final int value;
diff --git a/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/UnderlinePatterns.java b/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/UnderlinePatterns.java
index 0e27f429f3..05eb5d422f 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/UnderlinePatterns.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/UnderlinePatterns.java
@@ -16,6 +16,7 @@
 ==================================================================== */
 package org.apache.poi.xwpf.usermodel;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -133,12 +134,14 @@ public enum UnderlinePatterns {
      */
     NONE(18);
 
-    private static Map<Integer, UnderlinePatterns> imap = new HashMap<>();
+    private static final Map<Integer, UnderlinePatterns> imap;
 
     static {
+        final Map<Integer, UnderlinePatterns> tempMap = new HashMap<>();
         for (UnderlinePatterns p : values()) {
-            imap.put(p.getValue(), p);
+            tempMap.put(p.getValue(), p);
         }
+        imap = Collections.unmodifiableMap(tempMap);
     }
 
     private final int value;