diff --git a/server/src/main/java/org/elasticsearch/common/settings/SettingsModule.java b/server/src/main/java/org/elasticsearch/common/settings/SettingsModule.java
index 094ce5349b862..adef9fec912f8 100644
--- a/server/src/main/java/org/elasticsearch/common/settings/SettingsModule.java
+++ b/server/src/main/java/org/elasticsearch/common/settings/SettingsModule.java
@@ -63,11 +63,27 @@ public SettingsModule(
             List<Setting<?>> additionalSettings,
             List<String> settingsFilter,
             Set<SettingUpgrader<?>> settingUpgraders) {
+        this(
+            settings,
+            additionalSettings,
+            settingsFilter,
+            settingUpgraders,
+            ClusterSettings.BUILT_IN_CLUSTER_SETTINGS,
+            IndexScopedSettings.BUILT_IN_INDEX_SETTINGS);
+    }
+
+    SettingsModule(
+        final Settings settings,
+        final List<Setting<?>> additionalSettings,
+        final List<String> settingsFilter,
+        final Set<SettingUpgrader<?>> settingUpgraders,
+        final Set<Setting<?>> registeredClusterSettings,
+        final Set<Setting<?>> registeredIndexSettings) {
         this.settings = settings;
-        for (Setting<?> setting : ClusterSettings.BUILT_IN_CLUSTER_SETTINGS) {
+        for (Setting<?> setting : registeredClusterSettings) {
             registerSetting(setting);
         }
-        for (Setting<?> setting : IndexScopedSettings.BUILT_IN_INDEX_SETTINGS) {
+        for (Setting<?> setting : registeredIndexSettings) {
             registerSetting(setting);
         }
 
@@ -143,7 +159,7 @@ public SettingsModule(
         // by now we are fully configured, lets check node level settings for unregistered index settings
         clusterSettings.validate(settings, true);
         this.settingsFilter = new SettingsFilter(settingsFilterPattern);
-     }
+    }
 
     @Override
     public void configure(Binder binder) {
@@ -159,6 +175,9 @@ public void configure(Binder binder) {
      * the setting during startup.
      */
     private void registerSetting(Setting<?> setting) {
+        if (setting.getKey().contains(".") == false) {
+            throw new IllegalArgumentException("setting [" + setting.getKey() + "] is not in any namespace, its name must contain a dot");
+        }
         if (setting.isFiltered()) {
             if (settingsFilterPattern.contains(setting.getKey()) == false) {
                 registerSettingsFilter(setting.getKey());
diff --git a/server/src/test/java/org/elasticsearch/common/settings/SettingsModuleTests.java b/server/src/test/java/org/elasticsearch/common/settings/SettingsModuleTests.java
index 42c846d01f5a5..9f2ed63b6da61 100644
--- a/server/src/test/java/org/elasticsearch/common/settings/SettingsModuleTests.java
+++ b/server/src/test/java/org/elasticsearch/common/settings/SettingsModuleTests.java
@@ -24,9 +24,13 @@
 import org.hamcrest.Matchers;
 
 import java.util.Arrays;
+import java.util.List;
+import java.util.Set;
+import java.util.function.Supplier;
 
 import static java.util.Collections.emptySet;
 import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.hasToString;
 import static org.hamcrest.Matchers.is;
 
 public class SettingsModuleTests extends ModuleTestCase {
@@ -185,4 +189,31 @@ public void testMutuallyExclusiveScopes() {
             assertThat(e.getMessage(), containsString("Cannot register setting [foo.bar] twice"));
         }
     }
+
+    public void testPluginSettingWithoutNamespace() {
+        final String key = randomAlphaOfLength(8);
+        final Setting<String> setting = Setting.simpleString(key, Property.NodeScope);
+        runSettingWithoutNamespaceTest(
+            key, () -> new SettingsModule(Settings.EMPTY, List.of(setting), List.of(), Set.of(), Set.of(), Set.of()));
+    }
+
+    public void testClusterSettingWithoutNamespace() {
+        final String key = randomAlphaOfLength(8);
+        final Setting<String> setting = Setting.simpleString(key, Property.NodeScope);
+        runSettingWithoutNamespaceTest(
+            key, () -> new SettingsModule(Settings.EMPTY, List.of(), List.of(), Set.of(), Set.of(setting), Set.of()));
+    }
+
+    public void testIndexSettingWithoutNamespace() {
+        final String key = randomAlphaOfLength(8);
+        final Setting<String> setting = Setting.simpleString(key, Property.IndexScope);
+        runSettingWithoutNamespaceTest(
+            key, () -> new SettingsModule(Settings.EMPTY, List.of(), List.of(), Set.of(), Set.of(), Set.of(setting)));
+    }
+
+    private void runSettingWithoutNamespaceTest(final String key, final Supplier<SettingsModule> supplier) {
+        final IllegalArgumentException e = expectThrows(IllegalArgumentException.class, supplier::get);
+        assertThat(e, hasToString(containsString("setting [" + key + "] is not in any namespace, its name must contain a dot")));
+    }
+
 }