diff --git a/bundles/org.eclipse.e4.ui.workbench/META-INF/MANIFEST.MF b/bundles/org.eclipse.e4.ui.workbench/META-INF/MANIFEST.MF
index 844d05c5e48..e2fe621770f 100644
--- a/bundles/org.eclipse.e4.ui.workbench/META-INF/MANIFEST.MF
+++ b/bundles/org.eclipse.e4.ui.workbench/META-INF/MANIFEST.MF
@@ -1,7 +1,7 @@
 Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-SymbolicName: org.eclipse.e4.ui.workbench;singleton:=true
-Bundle-Version: 1.18.200.qualifier
+Bundle-Version: 1.18.300.qualifier
 Bundle-Name: %pluginName
 Bundle-Vendor: %providerName
 Bundle-Localization: plugin
diff --git a/bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/ModelAssembler.java b/bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/ModelAssembler.java
index 5965a64d48c..581e1243588 100644
--- a/bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/ModelAssembler.java
+++ b/bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/ModelAssembler.java
@@ -39,6 +39,8 @@
 import java.util.TreeSet;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 import org.eclipse.core.runtime.IConfigurationElement;
 import org.eclipse.core.runtime.IExtension;
 import org.eclipse.core.runtime.IExtensionPoint;
@@ -209,6 +211,8 @@ public void removedBundle(Bundle bundle, BundleEvent event, List<FragmentWrapper
 
 	private final List<ServiceReference<IModelProcessorContribution>> processorContributions = new CopyOnWriteArrayList<>();
 
+	private static final Pattern MESSAGE_FORMAT_BRACKETS_PATTERN = Pattern.compile("\\{\\}"); //$NON-NLS-1$
+
 	private BundleContext bundleContext;
 
 	private BundleTracker<List<FragmentWrapperElementMapping>> tracker;
@@ -820,7 +824,7 @@ private void log(LogMethod logMethod, PrintStream stream, String message, Object
 			logMethod.invoke(log, message, args);
 		} else {
 			// fallback if no LogService is available
-			stream.println(MessageFormat.format(message, args));
+			stream.println(MessageFormat.format(addIndex(message), args));
 		}
 	}
 
@@ -845,4 +849,20 @@ public void unsetLogger(LoggerFactory loggerFactory) {
 			this.logger = null;
 		}
 	}
+
+	/**
+	 * Adds missing indices to {@code {}} sequences in {@code format}. See:
+	 * {@link com.sun.org.slf4j.internal.Logger#addIndex(String)}
+	 */
+	private static String addIndex(String format) {
+		Matcher matcher = MESSAGE_FORMAT_BRACKETS_PATTERN.matcher(format);
+		StringBuilder sb = new StringBuilder();
+		int index = 0;
+		while (matcher.find()) {
+			String r = "{" + Integer.toString(index++) + "}"; //$NON-NLS-1$ //$NON-NLS-2$
+			matcher.appendReplacement(sb, r);
+		}
+		matcher.appendTail(sb);
+		return sb.toString();
+	}
 }