diff --git a/org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/diagnostics/DiagnosticsTest.java b/org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/diagnostics/DiagnosticsTest.java
index 1f4f4fd0c..138086ff1 100644
--- a/org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/diagnostics/DiagnosticsTest.java
+++ b/org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/diagnostics/DiagnosticsTest.java
@@ -104,7 +104,8 @@ public void testDiagnostics() throws CoreException {
 			assertEquals(markerCharStart, MarkerUtilities.getCharStart(marker.get()));
 			assertEquals(markerCharEnd, MarkerUtilities.getCharEnd(marker.get()));
 			assertEquals(markerLineIndex + 1, MarkerUtilities.getLineNumber(marker.get()));
-			assertEquals(diagnostic.getMessage(), MarkerUtilities.getMessage(marker.get()));
+			assertEquals(diagnostic.getMessage() + " [" + diagnostic.getCode().get() + "]",
+					MarkerUtilities.getMessage(marker.get()));
 		}
 
 		diagnosticsToMarkers.accept(new PublishDiagnosticsParams(file.getLocationURI().toString(), Collections.emptyList()));
@@ -229,7 +230,8 @@ public void testDiagnosticsRangeAfterDocument() throws CoreException {
 			Diagnostic diagnostic = diagnostics.get(i);
 			IMarker marker = markers[i];
 
-			assertEquals(diagnostic.getMessage(), MarkerUtilities.getMessage(marker));
+			assertEquals(diagnostic.getMessage() + " [" + diagnostic.getCode().get() + "]",
+					MarkerUtilities.getMessage(marker));
 			assertEquals(content.length(), MarkerUtilities.getCharStart(marker));
 			assertEquals(content.length(), MarkerUtilities.getCharEnd(marker));
 			assertEquals(1, MarkerUtilities.getLineNumber(marker));
diff --git a/org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/diagnostics/DiagnosticAnnotation.java b/org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/diagnostics/DiagnosticAnnotation.java
index 1f5fa337a..7166d272e 100644
--- a/org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/diagnostics/DiagnosticAnnotation.java
+++ b/org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/diagnostics/DiagnosticAnnotation.java
@@ -40,7 +40,7 @@ public void setType(@Nullable String type) {
 
 	@Override
 	public String getText() {
-		return this.diagnostic.getMessage();
+		return LSPDiagnosticsToMarkers.computeMarkerMessage(diagnostic);
 	}
 
 	@Override
diff --git a/org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/diagnostics/LSPDiagnosticsToMarkers.java b/org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/diagnostics/LSPDiagnosticsToMarkers.java
index 28acb0d68..fb93cff0e 100644
--- a/org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/diagnostics/LSPDiagnosticsToMarkers.java
+++ b/org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/diagnostics/LSPDiagnosticsToMarkers.java
@@ -58,6 +58,14 @@ public class LSPDiagnosticsToMarkers implements Consumer<PublishDiagnosticsParam
 	public static final String LSP_DIAGNOSTIC = "lspDiagnostic"; //$NON-NLS-1$
 	public static final String LANGUAGE_SERVER_ID = "languageServerId"; //$NON-NLS-1$
 	public static final String LS_DIAGNOSTIC_MARKER_TYPE = "org.eclipse.lsp4e.diagnostic"; //$NON-NLS-1$
+
+	static String computeMarkerMessage(final Diagnostic diagnostic) {
+		final Either<String, Integer> code = diagnostic.getCode();
+		return code == null //
+				? diagnostic.getMessage()
+				: diagnostic.getMessage() + " [" + code.get() + "]"; //$NON-NLS-1$ //$NON-NLS-2$
+	}
+
 	private final String languageServerId;
 	private final String markerType;
 	private final Optional<IMarkerAttributeComputer> markerAttributeComputer;
@@ -220,6 +228,7 @@ protected void updateMarker(Map<String, Object> targetAttributes, IMarker marker
 			return null;
 		}
 
+		final var markerMessage = computeMarkerMessage(diagnostic);
 		for (IMarker marker : remainingMarkers) {
 			if (!marker.exists()) {
 				continue;
@@ -227,7 +236,7 @@ protected void updateMarker(Map<String, Object> targetAttributes, IMarker marker
 			try {
 				if (LSPEclipseUtils.toOffset(diagnostic.getRange().getStart(), document) == MarkerUtilities.getCharStart(marker)
 						&& (LSPEclipseUtils.toOffset(diagnostic.getRange().getEnd(), document) == MarkerUtilities.getCharEnd(marker) || Objects.equals(diagnostic.getRange().getStart(), diagnostic.getRange().getEnd()))
-						&& Objects.equals(marker.getAttribute(IMarker.MESSAGE), diagnostic.getMessage())
+						&& Objects.equals(marker.getAttribute(IMarker.MESSAGE), markerMessage)
 						&& Objects.equals(marker.getAttribute(LANGUAGE_SERVER_ID), this.languageServerId)) {
 					return marker;
 				}
@@ -251,7 +260,7 @@ private Map<String, Object> computeMarkerAttributes(@Nullable IDocument document
 		final var attributes = new HashMap<String, Object>(8);
 		attributes.put(LSP_DIAGNOSTIC, diagnostic);
 		attributes.put(LANGUAGE_SERVER_ID, languageServerId);
-		attributes.put(IMarker.MESSAGE, diagnostic.getMessage());
+		attributes.put(IMarker.MESSAGE, computeMarkerMessage(diagnostic));
 		attributes.put(IMarker.SEVERITY, LSPEclipseUtils.toEclipseMarkerSeverity(diagnostic.getSeverity()));
 
 		if (document != null) {