diff --git a/gradle/changelog/plugin_installation_conflict.yaml b/gradle/changelog/plugin_installation_conflict.yaml
new file mode 100644
index 0000000000..a06f0eedec
--- /dev/null
+++ b/gradle/changelog/plugin_installation_conflict.yaml
@@ -0,0 +1,2 @@
+- type: fixed
+  description: Plugin installation conflict ([#2138](https://github.com/scm-manager/scm-manager/pull/2138))
diff --git a/scm-webapp/src/main/java/sonia/scm/plugin/DefaultPluginManager.java b/scm-webapp/src/main/java/sonia/scm/plugin/DefaultPluginManager.java
index 256f73eb9a..fd47cf5fdf 100644
--- a/scm-webapp/src/main/java/sonia/scm/plugin/DefaultPluginManager.java
+++ b/scm-webapp/src/main/java/sonia/scm/plugin/DefaultPluginManager.java
@@ -357,7 +357,13 @@ public class DefaultPluginManager implements PluginManager {
       }
     }
 
-    plugins.add(plugin);
+    if (pluginWasNotAddedYet(plugins, plugin)) {
+      plugins.add(plugin);
+    }
+  }
+
+  private static boolean pluginWasNotAddedYet(List<AvailablePlugin> plugins, AvailablePlugin plugin) {
+    return plugins.stream().noneMatch(p -> p.getDescriptor().getInformation().getName().equals(plugin.getDescriptor().getInformation().getName()));
   }
 
   private boolean isInstalledOrPending(String name) {
diff --git a/scm-webapp/src/test/java/sonia/scm/plugin/DefaultPluginManagerTest.java b/scm-webapp/src/test/java/sonia/scm/plugin/DefaultPluginManagerTest.java
index 74ec7a0d14..698e2cfd40 100644
--- a/scm-webapp/src/test/java/sonia/scm/plugin/DefaultPluginManagerTest.java
+++ b/scm-webapp/src/test/java/sonia/scm/plugin/DefaultPluginManagerTest.java
@@ -242,6 +242,24 @@ class DefaultPluginManagerTest {
       verify(installer).install(context, review);
     }
 
+    @Test
+    void shouldInstallMultipleSameDependingPluginsOnlyOnce() {
+      AvailablePlugin review = createAvailable("scm-review-plugin");
+      AvailablePlugin ci = createAvailable("scm-ci-plugin", "1.1.0");
+      InstalledPlugin oldCi = createInstalled("scm-ci-plugin", "1.0.0");
+      when(review.getDescriptor().getDependencies()).thenReturn(ImmutableSet.of("scm-mail-plugin", "scm-ci-plugin"));
+      AvailablePlugin mail = createAvailable("scm-mail-plugin");
+      when(mail.getDescriptor().getOptionalDependencies()).thenReturn(ImmutableSet.of("scm-ci-plugin"));
+      when(center.getAvailablePlugins()).thenReturn(ImmutableSet.of(review, mail, ci));
+      when(loader.getInstalledPlugins()).thenReturn(ImmutableSet.of(oldCi));
+
+      manager.install("scm-review-plugin", false);
+
+      verify(installer).install(context, mail);
+      verify(installer).install(context, review);
+      verify(installer, times(1)).install(context, ci);
+    }
+
     @Test
     void shouldNotInstallAlreadyInstalledDependenciesWhenUpToDate() {
       AvailablePlugin review = createAvailable("scm-review-plugin");