diff --git a/resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/ProjectDescription.java b/resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/ProjectDescription.java
index 5a1b5d02f6c..69c5e408513 100644
--- a/resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/ProjectDescription.java
+++ b/resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/ProjectDescription.java
@@ -24,6 +24,7 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.LinkedList;
 import java.util.List;
@@ -581,7 +582,7 @@ public boolean hasPrivateChanges(ProjectDescription description) {
 			return true;
 		}
 		// has natures changed?
-		if (!Set.of(natures).equals(Set.of(description.natures))) {
+		if (!new HashSet<>(Arrays.asList(natures)).equals(new HashSet<>(Arrays.asList(description.natures)))) {
 			return true;
 		}
 		// has buildspec changed?
diff --git a/resources/tests/org.eclipse.core.tests.resources/src/org/eclipse/core/tests/resources/NatureTest.java b/resources/tests/org.eclipse.core.tests.resources/src/org/eclipse/core/tests/resources/NatureTest.java
index c5483cd4bc9..d4c82a80eae 100644
--- a/resources/tests/org.eclipse.core.tests.resources/src/org/eclipse/core/tests/resources/NatureTest.java
+++ b/resources/tests/org.eclipse.core.tests.resources/src/org/eclipse/core/tests/resources/NatureTest.java
@@ -167,6 +167,30 @@ public void testInvalidRemovals() throws Throwable {
 		assertHasEnabledNature(NATURE_SNOW);
 	}
 
+	/**
+	 * Tests that duplicate natures in the project description don't cause
+	 * IllegalArgumentException. This is a regression test for a bug where
+	 * Set.of() was used which throws on duplicates.
+	 */
+	@Test
+	public void testDuplicateNatures() throws Throwable {
+		createInWorkspace(project);
+
+		// Set initial nature
+		setNatures(project, new String[] { NATURE_SIMPLE }, false);
+		assertHasEnabledNature(NATURE_SIMPLE);
+
+		// Try to set natures with a duplicate - this should not throw IllegalArgumentException
+		// The duplicate should be handled gracefully (deduplication happens automatically)
+		IProjectDescription desc = project.getDescription();
+		desc.setNatureIds(new String[] { NATURE_SIMPLE, NATURE_SIMPLE });
+		// This should not throw IllegalArgumentException when hasPrivateChanges is called
+		project.setDescription(desc, IResource.KEEP_HISTORY, createTestMonitor());
+		
+		// After deduplication, only one instance of the nature should remain
+		assertHasEnabledNature(NATURE_SIMPLE);
+	}
+
 	@Test
 	public void testNatureLifecyle() throws Throwable {
 		createInWorkspace(project);