diff --git a/scm-core/src/main/java/sonia/scm/repository/api/MergeStrategyNotSupportedException.java b/scm-core/src/main/java/sonia/scm/repository/api/MergeStrategyNotSupportedException.java
new file mode 100644
index 0000000000..ae9fbb08b4
--- /dev/null
+++ b/scm-core/src/main/java/sonia/scm/repository/api/MergeStrategyNotSupportedException.java
@@ -0,0 +1,27 @@
+package sonia.scm.repository.api;
+
+import sonia.scm.BadRequestException;
+import sonia.scm.repository.Repository;
+
+import static sonia.scm.ContextEntry.ContextBuilder.entity;
+
+@SuppressWarnings("squid:MaximumInheritanceDepth") // exceptions have a deep inheritance depth themselves; therefore we accept this here
+public class MergeStrategyNotSupportedException extends BadRequestException {
+
+  private static final long serialVersionUID = 256498734456613496L;
+
+  private static final String CODE = "6eRhF9gU41";
+
+  public MergeStrategyNotSupportedException(Repository repository, MergeStrategy strategy) {
+    super(entity(repository).build(), createMessage(strategy));
+  }
+
+  @Override
+  public String getCode() {
+    return CODE;
+  }
+
+  private static String createMessage(MergeStrategy strategy) {
+    return "merge strategy " + strategy + " is not supported by this repository";
+  }
+}
diff --git a/scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/GitMergeCommand.java b/scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/GitMergeCommand.java
index 27b4143b41..226dd0f285 100644
--- a/scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/GitMergeCommand.java
+++ b/scm-plugins/scm-git-plugin/src/main/java/sonia/scm/repository/spi/GitMergeCommand.java
@@ -8,6 +8,7 @@ import sonia.scm.repository.InternalRepositoryException;
 import sonia.scm.repository.api.MergeCommandResult;
 import sonia.scm.repository.api.MergeDryRunCommandResult;
 import sonia.scm.repository.api.MergeStrategy;
+import sonia.scm.repository.api.MergeStrategyNotSupportedException;
 
 import java.io.IOException;
 import java.util.Set;
@@ -46,7 +47,7 @@ public class GitMergeCommand extends AbstractGitCommand implements MergeCommand
         return inClone(clone -> new GitMergeCommit(clone, request, context, repository), workdirFactory, request.getTargetBranch());
 
       default:
-        throw new IllegalArgumentException("unknown merge strategy: " + request.getMergeStrategy());
+        throw new MergeStrategyNotSupportedException(repository, request.getMergeStrategy());
     }
   }
 
diff --git a/scm-webapp/src/main/resources/locales/de/plugins.json b/scm-webapp/src/main/resources/locales/de/plugins.json
index 2e36e60312..fe97d296c4 100644
--- a/scm-webapp/src/main/resources/locales/de/plugins.json
+++ b/scm-webapp/src/main/resources/locales/de/plugins.json
@@ -183,6 +183,10 @@
     "65RdZ5atX1": {
       "displayName": "Fehler beim Löschen von Plugin-Dateien",
       "description": "Einige Dateien für die Plugin-Deinstallation konnten nicht gelöscht werden. Dieses kann zu Inkonsistenzen führen, so dass der SCM-Manager nicht mehr korrekt starten kann. Bitte prüfen Sie die Logs und bereinigen Sie das Plugin-Verzeichnis des SCM-Managers manuell. Um die Installation eines Plugins abzubrechen, löschen Sie die zugehörige smp Datei aus dem Plugin-Verzeichnis. Um ein Entfernen eines Plugins zu verhindern, entfernen Sie die Datei namens 'uninstall' aus dem entsprechenden Verzeichnis des Plugins."
+    },
+    "6eRhF9gU41": {
+      "displayName": "Nicht unterstützte Merge-Strategie",
+      "description": "Die gewählte Merge-Strategie wird von dem Repository nicht unterstützt."
     }
   },
   "namespaceStrategies": {
diff --git a/scm-webapp/src/main/resources/locales/en/plugins.json b/scm-webapp/src/main/resources/locales/en/plugins.json
index 11643c4a70..27171374c9 100644
--- a/scm-webapp/src/main/resources/locales/en/plugins.json
+++ b/scm-webapp/src/main/resources/locales/en/plugins.json
@@ -183,6 +183,10 @@
     "65RdZ5atX1": {
       "displayName": "Error removing plugin files",
       "description": "Some files to cancel the plugin (un)installation could not be deleted. This can lead to inconsistencies so that the SCM-Manager cannot restart properly. Please check the logs and clean up the plugin folder manually. To cancel the installation of a plugin, remove the corresponding smp file. To cancel the uninstallation, remove the file named 'uninstall' inside the directory for this plugin."
+    },
+    "6eRhF9gU41": {
+      "displayName": "Merge strategy not supported",
+      "description": "The selected merge strategy is not supported by the repository."
     }
   },
   "namespaceStrategies": {