diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 35967a1ffd8e0..777129873edd8 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -79,7 +79,7 @@ Once your changes and tests are ready to submit for review:
 1. Test your changes
 
     Run the test suite to make sure that nothing is broken. See the
-[TESTING](TESTING.asciidoc) file for help running tests.
+[TESTING](TESTING.asciidoc) file for helping run tests.
 
 2. Sign the Contributor License Agreement
 
diff --git a/modules/analysis-common/src/yamlRestTest/resources/rest-api-spec/test/indices.analyze/10_analyze.yml b/modules/analysis-common/src/yamlRestTest/resources/rest-api-spec/test/indices.analyze/10_analyze.yml
index 971f530cebeb5..78fa5c0393d65 100644
--- a/modules/analysis-common/src/yamlRestTest/resources/rest-api-spec/test/indices.analyze/10_analyze.yml
+++ b/modules/analysis-common/src/yamlRestTest/resources/rest-api-spec/test/indices.analyze/10_analyze.yml
@@ -59,3 +59,22 @@
     - match:  { detail.tokenizer.tokens.0.token: ABc }
     - match:  { detail.tokenfilters.0.name: lowercase }
     - match:  { detail.tokenfilters.0.tokens.0.token: abc }
+
+---
+"Custom analyzer with unsupported param in request":
+  - do:
+      catch: bad_request
+      indices.create:
+        index: test
+        body:
+          settings:
+            analysis:
+              analyzer:
+                my_analyzer:
+                  type: custom
+                  tokenizer: standard
+                  foo: bar
+
+  - match: { status: 400 }
+  - match: { error.type: illegal_argument_exception }
+  - match: { error.reason: "Custom analyzer [my_analyzer] does not support [foo]" }
diff --git a/server/src/main/java/org/elasticsearch/index/analysis/AnalysisRegistry.java b/server/src/main/java/org/elasticsearch/index/analysis/AnalysisRegistry.java
index 9a185bc584066..03a355ef5b6b0 100644
--- a/server/src/main/java/org/elasticsearch/index/analysis/AnalysisRegistry.java
+++ b/server/src/main/java/org/elasticsearch/index/analysis/AnalysisRegistry.java
@@ -62,6 +62,7 @@ public final class AnalysisRegistry implements Closeable {
     private final Map<String, AnalysisProvider<TokenizerFactory>> tokenizers;
     private final Map<String, AnalysisProvider<AnalyzerProvider<?>>> analyzers;
     private final Map<String, AnalysisProvider<AnalyzerProvider<?>>> normalizers;
+    private static final Version CUSTOM_ANALYZER_KEY_CHECK_VERSION = Version.V_8_5_0;
 
     public AnalysisRegistry(
         Environment environment,
@@ -459,6 +460,14 @@ private <T> Map<String, T> buildMapping(
             Settings currentSettings = entry.getValue();
             String typeName = currentSettings.get("type");
             if (component == Component.ANALYZER) {
+                if (settings.getIndexVersionCreated().onOrAfter(CUSTOM_ANALYZER_KEY_CHECK_VERSION)) {
+                    for (String key : currentSettings.keySet()) {
+                        switch (key) {
+                            case "tokenizer", "char_filter", "filter", "type", "position_increment_gap" -> {}
+                            default -> throw new IllegalArgumentException("Custom analyzer [" + name + "] does not support [" + key + "]");
+                        }
+                    }
+                }
                 T factory = null;
                 if (typeName == null) {
                     if (currentSettings.get("tokenizer") != null) {
diff --git a/server/src/test/java/org/elasticsearch/index/analysis/AnalysisTests.java b/server/src/test/java/org/elasticsearch/index/analysis/AnalysisTests.java
index ac1a455a3cdff..b272cdfa1942d 100644
--- a/server/src/test/java/org/elasticsearch/index/analysis/AnalysisTests.java
+++ b/server/src/test/java/org/elasticsearch/index/analysis/AnalysisTests.java
@@ -9,10 +9,14 @@
 package org.elasticsearch.index.analysis;
 
 import org.apache.lucene.analysis.CharArraySet;
+import org.elasticsearch.Version;
+import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.env.Environment;
 import org.elasticsearch.env.TestEnvironment;
+import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.IndexSettingsModule;
 
 import java.io.BufferedWriter;
 import java.io.FileNotFoundException;
@@ -27,6 +31,7 @@
 import java.util.Arrays;
 import java.util.List;
 
+import static java.util.Collections.emptyMap;
 import static org.hamcrest.Matchers.is;
 
 public class AnalysisTests extends ESTestCase {
@@ -103,4 +108,36 @@ public void testParseWordList() throws IOException {
         List<String> wordList = Analysis.getWordList(env, nodeSettings, "foo.bar");
         assertEquals(Arrays.asList("hello", "world"), wordList);
     }
+
+    public void testCustomAnalyzerWithUnsupportedKey() {
+        Settings analyzerSettings = Settings.builder().
+            put("index.analysis.analyzer.my_analyzer.tokenizer", "standard").
+            put("index.analysis.analyzer.my_analyzer.type", "custom").
+            put("index.analysis.analyzer.my_analyzer.foo", "bar").
+            build();
+        Settings settings = Settings.builder().
+            put(IndexMetadata.SETTING_VERSION_CREATED, Version.V_8_5_0).
+            put(Environment.PATH_HOME_SETTING.getKey(), createTempDir().toString()).
+            put(analyzerSettings).
+            build();
+
+        IndexSettings idxSettings = IndexSettingsModule.newIndexSettings("index", settings);
+        AnalysisRegistry emptyAnalysisRegistry = new AnalysisRegistry(
+            TestEnvironment.newEnvironment(settings),
+            emptyMap(),
+            emptyMap(),
+            emptyMap(),
+            emptyMap(),
+            emptyMap(),
+            emptyMap(),
+            emptyMap(),
+            emptyMap(),
+            emptyMap()
+        );
+        IllegalArgumentException ex = expectThrows(
+            IllegalArgumentException.class,
+            () -> emptyAnalysisRegistry.build(idxSettings)
+        );
+        assertEquals(ex.getMessage(), "Custom analyzer [my_analyzer] does not support [foo]");
+    }
 }