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 6fe9b8e3e..671801e09 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
@@ -40,6 +40,10 @@ import org.springframework.ide.vscode.commons.util.BadLocationException;
 import org.springframework.ide.vscode.commons.util.Futures;
 import org.springframework.ide.vscode.commons.util.text.TextDocument;
 
+import reactor.core.publisher.Mono;
+import reactor.core.scheduler.Scheduler;
+import reactor.core.scheduler.Schedulers;
+
 /**
  * Abstract base class to implement LanguageServer. Bits and pieces copied from
  * the 'JavaLanguageServer' example which seem generally useful / reusable end up in
@@ -50,6 +54,8 @@ public abstract class SimpleLanguageServer implements LanguageServer, LanguageCl
 
     private static final Logger LOG = Logger.getLogger(SimpleLanguageServer.class.getName());
 
+	private static final Scheduler RECONCILER_SCHEDULER = Schedulers.newSingle("Reconciler");
+
     private Path workspaceRoot;
 
 	private SimpleTextDocumentService tds;
@@ -65,6 +71,8 @@ public abstract class SimpleLanguageServer implements LanguageServer, LanguageCl
 		}
 	};
 
+	private CompletableFuture<Void> busyReconcile = CompletableFuture.completedFuture(null);
+
 	@Override
 	public void connect(LanguageClient _client) {
 		this.client = (STS4LanguageClient) _client;
@@ -150,7 +158,10 @@ public abstract class SimpleLanguageServer implements LanguageServer, LanguageCl
 	 * Convenience method. Subclasses can call this to use a {@link IReconcileEngine} ported
 	 * from old STS codebase to validate a given {@link TextDocument} and publish Diagnostics.
 	 */
-	protected void validateWith(TextDocument doc, IReconcileEngine engine) {
+	protected void validateWith(TextDocument _doc, IReconcileEngine engine) {
+		TextDocument doc = _doc.copy();
+
+		this.busyReconcile = new CompletableFuture<Void>();
 
 		SimpleTextDocumentService documents = getTextDocumentService();
 		IProblemCollector problems = new IProblemCollector() {
@@ -198,7 +209,23 @@ public abstract class SimpleLanguageServer implements LanguageServer, LanguageCl
 				}
 			}
 		};
-		engine.reconcile(doc, problems);
+
+		// Avoid running in the same thread as lsp4j as it can result
+		// in long "hangs" for slow reconcile providers
+		Mono.fromRunnable(() -> {
+			engine.reconcile(doc, problems);
+		})
+		.doOnTerminate((ignore1, ignore2) -> {
+			busyReconcile.complete(null);
+		})
+		.subscribeOn(RECONCILER_SCHEDULER)
+		.subscribe();
+	}
+
+	public void waitForReconcile() throws Exception {
+		while (!this.busyReconcile.isDone()) {
+			this.busyReconcile.get();
+		}
 	}
 
 	public LanguageClient getClient() {
diff --git a/vscode-extensions/commons/language-server-test-harness/src/main/java/org/springframework/ide/vscode/languageserver/testharness/Editor.java b/vscode-extensions/commons/language-server-test-harness/src/main/java/org/springframework/ide/vscode/languageserver/testharness/Editor.java
index 20ea262e3..b87bb6334 100644
--- a/vscode-extensions/commons/language-server-test-harness/src/main/java/org/springframework/ide/vscode/languageserver/testharness/Editor.java
+++ b/vscode-extensions/commons/language-server-test-harness/src/main/java/org/springframework/ide/vscode/languageserver/testharness/Editor.java
@@ -221,7 +221,7 @@ public class Editor {
 			: "";
 	}
 
-	private List<Diagnostic> reconcile() {
+	private List<Diagnostic> reconcile() throws Exception {
 		// We assume the language server works synchronously for now and it does an immediate reconcile
 		// when the document changes. In the future this is probably not going to be the case though and then this
 		// method will need to somehow ensure the linter is done working before retrieving the problems from the
diff --git a/vscode-extensions/commons/language-server-test-harness/src/main/java/org/springframework/ide/vscode/languageserver/testharness/LanguageServerHarness.java b/vscode-extensions/commons/language-server-test-harness/src/main/java/org/springframework/ide/vscode/languageserver/testharness/LanguageServerHarness.java
index 3232da307..1294557a3 100644
--- a/vscode-extensions/commons/language-server-test-harness/src/main/java/org/springframework/ide/vscode/languageserver/testharness/LanguageServerHarness.java
+++ b/vscode-extensions/commons/language-server-test-harness/src/main/java/org/springframework/ide/vscode/languageserver/testharness/LanguageServerHarness.java
@@ -54,6 +54,7 @@ import org.eclipse.lsp4j.services.LanguageServer;
 import org.springframework.ide.vscode.commons.languageserver.LanguageIds;
 import org.springframework.ide.vscode.commons.languageserver.ProgressParams;
 import org.springframework.ide.vscode.commons.languageserver.STS4LanguageClient;
+import org.springframework.ide.vscode.commons.languageserver.util.SimpleLanguageServer;
 
 public class LanguageServerHarness {
 
@@ -61,10 +62,10 @@ public class LanguageServerHarness {
 
 	private Random random = new Random();
 
-	private Callable<? extends LanguageServer> factory;
+	private Callable<? extends SimpleLanguageServer> factory;
 	private String defaultLanguageId;
 
-	private LanguageServer server;
+	private SimpleLanguageServer server;
 
 	private InitializeResult initResult;
 
@@ -72,12 +73,12 @@ public class LanguageServerHarness {
 	private Map<String, PublishDiagnosticsParams> diagnostics = new HashMap<>();
 
 
-	public LanguageServerHarness(Callable<? extends LanguageServer> factory, String defaultLanguageId) {
+	public LanguageServerHarness(Callable<? extends SimpleLanguageServer> factory, String defaultLanguageId) {
 		this.factory = factory;
 		this.defaultLanguageId = defaultLanguageId;
 	}
 
-	public LanguageServerHarness(Callable<? extends LanguageServer> factory) throws Exception {
+	public LanguageServerHarness(Callable<? extends SimpleLanguageServer> factory) throws Exception {
 		this(factory, LanguageIds.PLAINTEXT);
 	}
 
@@ -263,7 +264,8 @@ public class LanguageServerHarness {
 		return TextDocumentSyncKind.None;
 	}
 
-	public PublishDiagnosticsParams getDiagnostics(TextDocumentInfo doc) {
+	public PublishDiagnosticsParams getDiagnostics(TextDocumentInfo doc) throws Exception {
+		this.server.waitForReconcile();
 		return diagnostics.get(doc.getUri());
 	}