diff --git a/src/java.naming/share/classes/com/sun/jndi/ldap/sasl/SaslOutputStream.java b/src/java.naming/share/classes/com/sun/jndi/ldap/sasl/SaslOutputStream.java
index 30d64fc8611..8787df8c498 100644
--- a/src/java.naming/share/classes/com/sun/jndi/ldap/sasl/SaslOutputStream.java
+++ b/src/java.naming/share/classes/com/sun/jndi/ldap/sasl/SaslOutputStream.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -35,9 +35,10 @@ import java.io.OutputStream;
 class SaslOutputStream extends FilterOutputStream {
     private static final boolean debug = false;
 
-    private byte[] lenBuf = new byte[4];  // buffer for storing length
+    private final byte[] lenBuf = new byte[4];  // buffer for storing length
     private int rawSendSize = 65536;
-    private SaslClient sc;
+    private final SaslClient sc;
+    private boolean closed;
 
     SaslOutputStream(SaslClient sc, OutputStream out) throws SaslException {
         super(out);
@@ -60,8 +61,9 @@ class SaslOutputStream extends FilterOutputStream {
 
     // Override this method to call write(byte[], int, int) counterpart
     // super.write(int) simply calls out.write(int)
-
+    @Override
     public void write(int b) throws IOException {
+        ensureOpen();
         byte[] buffer = new byte[1];
         buffer[0] = (byte)b;
         write(buffer, 0, 1);
@@ -71,7 +73,9 @@ class SaslOutputStream extends FilterOutputStream {
      * Override this method to "wrap" the outgoing buffer before
      * writing it to the underlying output stream.
      */
+    @Override
     public void write(byte[] buffer, int offset, int total) throws IOException {
+        ensureOpen();
         int count;
         byte[] wrappedToken;
 
@@ -101,7 +105,12 @@ class SaslOutputStream extends FilterOutputStream {
         }
     }
 
+    @Override
     public void close() throws IOException {
+        if (closed) {
+            return;
+        }
+        closed = true;
         SaslException save = null;
         try {
             sc.dispose();  // Dispose of SaslClient's state
@@ -121,8 +130,7 @@ class SaslOutputStream extends FilterOutputStream {
      * Encodes an integer into 4 bytes in network byte order in the buffer
      * supplied.
      */
-    private static void intToNetworkByteOrder(int num, byte[] buf, int start,
-        int count) {
+    private static void intToNetworkByteOrder(int num, byte[] buf, int start, int count) {
         if (count > 4) {
             throw new IllegalArgumentException("Cannot handle more than 4 bytes");
         }
@@ -132,4 +140,10 @@ class SaslOutputStream extends FilterOutputStream {
             num >>>= 8;
         }
     }
+
+    private void ensureOpen() throws IOException {
+        if (closed) {
+            throw new IOException("stream closed");
+        }
+    }
 }
diff --git a/test/jdk/com/sun/jndi/ldap/SaslOutputStreamCloseTest.java b/test/jdk/com/sun/jndi/ldap/SaslOutputStreamCloseTest.java
new file mode 100644
index 00000000000..5558a4ab196
--- /dev/null
+++ b/test/jdk/com/sun/jndi/ldap/SaslOutputStreamCloseTest.java
@@ -0,0 +1,130 @@
+/*
+ * Copyright (c) 2026, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.lang.reflect.Constructor;
+
+import javax.security.sasl.SaslClient;
+import javax.security.sasl.SaslException;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.fail;
+
+/*
+ * @test
+ * @bug 8377486
+ * @summary Verify that SaslOutputStream.write() methods throw an IOException, if invoked
+ *          when the stream is closed
+ * @modules java.security.sasl/com.sun.security.sasl
+ *          java.naming/com.sun.jndi.ldap.sasl:+open
+ * @run junit ${test.main.class}
+ */
+class SaslOutputStreamCloseTest {
+
+    /*
+     * Verifies that SaslOutputStream.write(...) throws IOException if the SaslOutputStream
+     * is closed.
+     */
+    @Test
+    void testWriteThrowsIOExceptionOnClose() throws Exception {
+        try (final OutputStream os = createSaslOutputStream(new ByteArrayOutputStream())) {
+            os.write(new byte[]{0x42, 0x42});
+            os.close();
+            try {
+                os.write(new byte[]{0x42}, 0, 1);
+                fail("OutputStream.write(...) on closed " + os + " did not throw IOException");
+            } catch (IOException ioe) {
+                // verify it was thrown for right reason
+                if (!"stream closed".equals(ioe.getMessage())) {
+                    throw ioe; // propagate original exception
+                }
+                // expected
+                System.err.println("received expected IOException: " + ioe);
+            }
+        }
+    }
+
+    // reflectively construct an instance of
+    // (package private) com.sun.jndi.ldap.sasl.SaslOutputStream class
+    private static OutputStream createSaslOutputStream(final OutputStream underlying) throws Exception {
+        final Constructor<?> constructor = Class.forName("com.sun.jndi.ldap.sasl.SaslOutputStream")
+                .getDeclaredConstructor(new Class[]{SaslClient.class, OutputStream.class});
+        constructor.setAccessible(true);
+        return (OutputStream) constructor.newInstance(new DummySaslClient(), underlying);
+    }
+
+
+    private static final class DummySaslClient implements SaslClient {
+        private boolean closed;
+
+        @Override
+        public String getMechanismName() {
+            return "DUMMY";
+        }
+
+        @Override
+        public boolean hasInitialResponse() {
+            return false;
+        }
+
+        @Override
+        public byte[] evaluateChallenge(byte[] challenge) throws SaslException {
+            return new byte[0];
+        }
+
+        @Override
+        public boolean isComplete() {
+            return true;
+        }
+
+        @Override
+        public byte[] unwrap(byte[] incoming, int offset, int len) throws SaslException {
+            if (closed) {
+                // intentionally throw something other than a IOException
+                throw new IllegalStateException(this + " is closed");
+            }
+            return incoming;
+        }
+
+        @Override
+        public byte[] wrap(byte[] outgoing, int offset, int len) throws SaslException {
+            if (closed) {
+                // intentionally throw something other than a IOException
+                throw new IllegalStateException(this + " is closed");
+            }
+            return outgoing;
+        }
+
+        @Override
+        public Object getNegotiatedProperty(String propName) {
+            return null;
+        }
+
+        @Override
+        public void dispose() {
+            this.closed = true;
+        }
+    }
+}