diff --git a/test/jdk/sun/security/util/KeyUtilTests.java b/test/jdk/sun/security/util/KeyUtilTests.java
new file mode 100644
index 00000000000..79863bdd8bf
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+++ b/test/jdk/sun/security/util/KeyUtilTests.java
@@ -0,0 +1,134 @@
+/*
+ * 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 jdk.test.lib.Asserts;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import sun.security.util.KeyUtil;
+
+import java.security.AlgorithmParameters;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.security.NoSuchAlgorithmException;
+import java.security.NoSuchProviderException;
+import java.security.Provider;
+import java.security.Security;
+import java.security.interfaces.ECPrivateKey;
+import java.security.spec.InvalidParameterSpecException;
+import java.util.ArrayList;
+import java.util.List;
+
+/*
+ * @test
+ * @summary Tests for sun.security.util.KeyUtil
+ * @library /test/lib
+ * @modules java.base/sun.security.util
+ * @run junit/othervm KeyUtilTests
+ */
+public class KeyUtilTests {
+
+    @BeforeAll
+    public static void setup() {
+        // Register the custom provider
+        Security.addProvider(new CustomSunEC());
+    }
+
+    @Test
+    public void testProvidersAdded() {
+        final List<String> providers = new ArrayList<>();
+        for (final Provider provider : Security.getProviders()) {
+            providers.add(provider.getName());
+        }
+        Assertions.assertTrue(providers.contains("CustomSunEC"));
+    }
+
+    @Test
+    public void testGetKeySizeCustomSunEc()
+            throws NoSuchAlgorithmException,
+            NoSuchProviderException,
+            InvalidParameterSpecException {
+
+        final int keySize = 256;
+
+        final KeyPairGenerator keyPairGenerator
+                = KeyPairGenerator.getInstance("EC", "CustomSunEC");
+        keyPairGenerator.initialize(keySize);
+        final KeyPair keyPair = keyPairGenerator.generateKeyPair();
+
+        final ECPrivateKey ecPrivateKey = (ECPrivateKey) keyPair.getPrivate();
+        final AlgorithmParameters params
+                = AlgorithmParameters.getInstance("EC", "CustomSunEC");
+        params.init(ecPrivateKey.getParams());
+
+        int keySizeResult = KeyUtil.getKeySize(params);
+        Asserts.assertEquals(keySizeResult, keySize, "Key size is");
+    }
+
+    @Test
+    public void testGetKeySizeSunEc()
+            throws NoSuchAlgorithmException,
+            NoSuchProviderException,
+            InvalidParameterSpecException {
+
+        final int keySize = 256;
+
+        final KeyPairGenerator keyPairGenerator
+                = KeyPairGenerator.getInstance("EC", "SunEC");
+        keyPairGenerator.initialize(keySize);
+        final KeyPair keyPair = keyPairGenerator.generateKeyPair();
+
+        final ECPrivateKey ecPrivateKey = (ECPrivateKey) keyPair.getPrivate();
+        final AlgorithmParameters params
+                = AlgorithmParameters.getInstance("EC", "SunEC");
+        params.init(ecPrivateKey.getParams());
+
+        int keySizeResult = KeyUtil.getKeySize(params);
+        Asserts.assertEquals(keySizeResult, keySize, "Key size is");
+    }
+
+
+}
+
+class CustomSunEC extends Provider {
+    public CustomSunEC() {
+        super("CustomSunEC",
+                "1.0",
+                "Custom SunEC Provider");
+
+        final Provider sunECProvider = Security.getProvider("SunEC");
+        if (sunECProvider != null) {
+            // Copy all service mappings from SunEC to CustomSunEC
+            sunECProvider.getServices().forEach(service ->
+                    putService(new Service(
+                            this,
+                            service.getType(),
+                            service.getAlgorithm(),
+                            service.getClassName(),
+                            null,
+                            null)));
+        }
+    }
+}
+
+