diff --git a/vscode-extensions/commons/commons-language-server/src/main/java/org/springframework/ide/vscode/commons/languageserver/util/SimpleLanguageServer.java b/vscode-extensions/commons/commons-language-server/src/main/java/org/springframework/ide/vscode/commons/languageserver/util/SimpleLanguageServer.java
index 671801e09..3191933a3 100644
--- a/vscode-extensions/commons/commons-language-server/src/main/java/org/springframework/ide/vscode/commons/languageserver/util/SimpleLanguageServer.java
+++ b/vscode-extensions/commons/commons-language-server/src/main/java/org/springframework/ide/vscode/commons/languageserver/util/SimpleLanguageServer.java
@@ -161,7 +161,7 @@ public abstract class SimpleLanguageServer implements LanguageServer, LanguageCl
 	protected void validateWith(TextDocument _doc, IReconcileEngine engine) {
 		TextDocument doc = _doc.copy();
 
-		this.busyReconcile = new CompletableFuture<Void>();
+		CompletableFuture<Void> reconcileSession = this.busyReconcile = new CompletableFuture<Void>();
 
 		SimpleTextDocumentService documents = getTextDocumentService();
 		IProblemCollector problems = new IProblemCollector() {
@@ -216,7 +216,7 @@ public abstract class SimpleLanguageServer implements LanguageServer, LanguageCl
 			engine.reconcile(doc, problems);
 		})
 		.doOnTerminate((ignore1, ignore2) -> {
-			busyReconcile.complete(null);
+			reconcileSession.complete(null);
 		})
 		.subscribeOn(RECONCILER_SCHEDULER)
 		.subscribe();
diff --git a/vscode-extensions/vscode-boot-properties/src/test/java/org/springframework/ide/vscode/boot/editor/harness/PropertyIndexHarness.java b/vscode-extensions/vscode-boot-properties/src/test/java/org/springframework/ide/vscode/boot/editor/harness/PropertyIndexHarness.java
index 58dbc9004..0a727548d 100644
--- a/vscode-extensions/vscode-boot-properties/src/test/java/org/springframework/ide/vscode/boot/editor/harness/PropertyIndexHarness.java
+++ b/vscode-extensions/vscode-boot-properties/src/test/java/org/springframework/ide/vscode/boot/editor/harness/PropertyIndexHarness.java
@@ -37,20 +37,23 @@ public class PropertyIndexHarness {
 	private SpringPropertyIndex index = null;
 	private IJavaProject testProject = null;
 
-	protected SpringPropertyIndexProvider indexProvider = new SpringPropertyIndexProvider() {
+	protected final SpringPropertyIndexProvider indexProvider = new SpringPropertyIndexProvider() {
+		@Override
 		public FuzzyMap<PropertyInfo> getIndex(IDocument doc) {
-			if (index==null) {
-				IClasspath classpath = testProject == null ? null : testProject.getClasspath();
-				index =	new SpringPropertyIndex(valueProviders, classpath);
-				for (ConfigurationMetadataProperty propertyInfo : datas.values()) {
-					index.add(propertyInfo);
+			synchronized (PropertyIndexHarness.this) {
+				if (index==null) {
+					IClasspath classpath = testProject == null ? null : testProject.getClasspath();
+					index =	new SpringPropertyIndex(valueProviders, classpath);
+					for (ConfigurationMetadataProperty propertyInfo : datas.values()) {
+						index.add(propertyInfo);
+					}
 				}
+				return index;
 			}
-			return index;
 		}
 	};
 
-	public void useProject(IJavaProject p) throws Exception {
+	public synchronized void useProject(IJavaProject p) throws Exception {
 		index = null;
 		this.testProject = p;
 	}
@@ -96,7 +99,7 @@ public class PropertyIndexHarness {
 	}
 
 
-	public ItemConfigurer data(String id, String type, Object deflt, String description,
+	public synchronized ItemConfigurer data(String id, String type, Object deflt, String description,
 			String... source
 	) {
 		ConfigurationMetadataProperty item = new ConfigurationMetadataProperty();
@@ -109,7 +112,7 @@ public class PropertyIndexHarness {
 		return new ItemConfigurer(item);
 	}
 
-	public void keyHints(String id, String... hintValues) {
+	public synchronized void keyHints(String id, String... hintValues) {
 		index = null;
 		List<ValueHint> hints = datas.get(id).getHints().getKeyHints();
 		for (String value : hintValues) {
@@ -119,7 +122,7 @@ public class PropertyIndexHarness {
 		}
 	}
 
-	public void valueHints(String id, String... hintValues) {
+	public synchronized void valueHints(String id, String... hintValues) {
 		index = null;
 		List<ValueHint> hints = datas.get(id).getHints().getValueHints();
 		for (String value : hintValues) {
@@ -129,7 +132,7 @@ public class PropertyIndexHarness {
 		}
 	}
 
-	public void deprecate(String key, String replacedBy, String reason) {
+	public synchronized void deprecate(String key, String replacedBy, String reason) {
 		index = null;
 		ConfigurationMetadataProperty info = datas.get(key);
 		Deprecation d = new Deprecation();