diff --git a/src/main/java/org/codelibs/jcifs/smb/impl/SmbTreeImpl.java b/src/main/java/org/codelibs/jcifs/smb/impl/SmbTreeImpl.java
index 66129108..c00d2ecc 100644
--- a/src/main/java/org/codelibs/jcifs/smb/impl/SmbTreeImpl.java
+++ b/src/main/java/org/codelibs/jcifs/smb/impl/SmbTreeImpl.java
@@ -22,11 +22,11 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.EnumSet;
-import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
@@ -94,7 +94,7 @@ class SmbTreeImpl implements SmbTreeInternal {
     private final List<StackTraceElement[]> acquires;
     private final List<StackTraceElement[]> releases;
 
-    private final Map<String, DfsReferralData> treeReferrals = new HashMap<>();
+    private final Map<String, DfsReferralData> treeReferrals = new ConcurrentHashMap<>();
 
     SmbTreeImpl(final SmbSessionImpl session, final String share, final String service) {
         this.session = session.acquire();