diff --git a/org.eclipse.xtend.ide.tests/src/org/eclipse/xtend/ide/tests/compiler/JavaVersionSettingTest.xtend b/org.eclipse.xtend.ide.tests/src/org/eclipse/xtend/ide/tests/compiler/JavaVersionSettingTest.xtend
index 9da0fe96f12..a869fddfc59 100644
--- a/org.eclipse.xtend.ide.tests/src/org/eclipse/xtend/ide/tests/compiler/JavaVersionSettingTest.xtend
+++ b/org.eclipse.xtend.ide.tests/src/org/eclipse/xtend/ide/tests/compiler/JavaVersionSettingTest.xtend
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2015, 2024 itemis AG (http://www.itemis.eu) and others.
+ * Copyright (c) 2015, 2026 itemis AG (http://www.itemis.eu) and others.
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License 2.0 which is available at
  * http://www.eclipse.org/legal/epl-2.0.
@@ -61,6 +61,7 @@ class JavaVersionSettingTest extends Assert {
 	@Test def void testCompileWithJava8() {
 		workbenchTestHelper.tearDown
 		WorkbenchTestHelper.createPluginProject(WorkbenchTestHelper.TESTPROJECT_NAME, JavaVersion.JAVA8)
+		waitForJdtIndex()
 		val xtendFile = workbenchTestHelper.createFile('mypackage/OverrideTest.xtend', '''
 			package mypackage
 			class B implements A {
@@ -94,4 +95,4 @@ class JavaVersionSettingTest extends Assert {
 		}
 	}
 	
-}
\ No newline at end of file
+}
diff --git a/org.eclipse.xtend.ide.tests/xtend-gen/org/eclipse/xtend/ide/tests/compiler/JavaVersionSettingTest.java b/org.eclipse.xtend.ide.tests/xtend-gen/org/eclipse/xtend/ide/tests/compiler/JavaVersionSettingTest.java
index 501fe0a1e82..4c357bb0c3a 100644
--- a/org.eclipse.xtend.ide.tests/xtend-gen/org/eclipse/xtend/ide/tests/compiler/JavaVersionSettingTest.java
+++ b/org.eclipse.xtend.ide.tests/xtend-gen/org/eclipse/xtend/ide/tests/compiler/JavaVersionSettingTest.java
@@ -1,5 +1,5 @@
 /**
- * Copyright (c) 2015, 2024 itemis AG (http://www.itemis.eu) and others.
+ * Copyright (c) 2015, 2026 itemis AG (http://www.itemis.eu) and others.
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License 2.0 which is available at
  * http://www.eclipse.org/legal/epl-2.0.
@@ -68,6 +68,7 @@ public void testCompileWithJava8() {
     try {
       this.workbenchTestHelper.tearDown();
       WorkbenchTestHelper.createPluginProject(WorkbenchTestHelper.TESTPROJECT_NAME, JavaVersion.JAVA8);
+      IResourcesSetupUtil.waitForJdtIndex();
       StringConcatenation _builder = new StringConcatenation();
       _builder.append("package mypackage");
       _builder.newLine();
diff --git a/org.eclipse.xtext.common.types.eclipse.tests/tests/org/eclipse/xtext/common/types/ui/notification/TypeResourceUnloaderTest.java b/org.eclipse.xtext.common.types.eclipse.tests/tests/org/eclipse/xtext/common/types/ui/notification/TypeResourceUnloaderTest.java
index 75648478d47..739207b369c 100644
--- a/org.eclipse.xtext.common.types.eclipse.tests/tests/org/eclipse/xtext/common/types/ui/notification/TypeResourceUnloaderTest.java
+++ b/org.eclipse.xtext.common.types.eclipse.tests/tests/org/eclipse/xtext/common/types/ui/notification/TypeResourceUnloaderTest.java
@@ -32,6 +32,7 @@
 import org.eclipse.xtext.resource.IEObjectDescription;
 import org.eclipse.xtext.resource.IResourceDescription;
 import org.eclipse.xtext.ui.notification.IStateChangeEventBroker;
+import org.eclipse.xtext.ui.testing.util.IResourcesSetupUtil;
 import org.eclipse.xtext.xbase.lib.Procedures;
 import org.eclipse.xtext.xbase.lib.Procedures.Procedure0;
 import org.junit.After;
@@ -78,8 +79,14 @@ public void setUp() throws Exception {
 		projectProvider = new MockJavaProjectProvider();
 		projectProvider.setUseSource(true);
 		project = projectProvider.getJavaProject(null);
+		// Ensure the JDT incremental builder state is fully populated before the test starts.
+		// Without this, JavaBuilderState.getDefinedTypeNamesFor(typeLocator) may return null
+		// and convertRemovedTypes(...) will only emit a delta for the primary type, causing
+		// e.g. testRenameClass to see 4 deltas instead of the expected 6.
+		IResourcesSetupUtil.waitForBuild();
 		type = project.findType(NESTED_TYPES);
 		compilationUnit = type.getCompilationUnit();
+		assertBuilderStateContainsNestedTypes();
 		compilationUnit.becomeWorkingCopy(null);
 		
 		// wait until the BackgroundThread for the reconciler was started
@@ -105,6 +112,9 @@ public void tearDown() throws Exception {
 		eventBroker = null;
 		projectProvider = null;
 		compilationUnit.discardWorkingCopy();
+		// Make sure the rebuild triggered by doSave above is finished before the next
+		// @Before runs, so that JavaBuilderState is consistent for the following test.
+		IResourcesSetupUtil.waitForBuild();
 		compilationUnit = null;
 		editor = null;
 		type = null;
@@ -112,6 +122,23 @@ public void tearDown() throws Exception {
 		event = null;
 		subsequentEvents = null;
 	}
+
+	/**
+	 * Sanity check that the JDT builder state knows about all three nested types defined in
+	 * {@code NestedTypes.java}. If this fails, the test environment is racing with the Java
+	 * builder and the actual test assertions would be misleading.
+	 */
+	private void assertBuilderStateContainsNestedTypes() {
+		JavaBuilderState builderState = JavaBuilderState.getLastBuiltState(project.getProject());
+		assertNotNull("No JDT builder state available for project " + project.getElementName(), builderState);
+		TypeNames typeNames = builderState.getQualifiedTypeNames(compilationUnit);
+		Collection<String> names = typeNames.getTypeNames();
+		assertTrue("Builder state is missing " + NESTED_TYPES + ", was: " + names, names.contains(NESTED_TYPES));
+		assertTrue("Builder state is missing " + NESTED_TYPES + "$Outer, was: " + names,
+				names.contains(NESTED_TYPES + "$Outer"));
+		assertTrue("Builder state is missing " + NESTED_TYPES + "$Outer$Inner, was: " + names,
+				names.contains(NESTED_TYPES + "$Outer$Inner"));
+	}
 	
 	@Test public void testNullChange() throws BadLocationException, InterruptedException {
 		waitForEvent(new Procedure0() {