diff --git a/http/http/src/main/java/io/helidon/http/ServerRequestHeaders.java b/http/http/src/main/java/io/helidon/http/ServerRequestHeaders.java
index b97ad8353a0..38cd32c9b9a 100644
--- a/http/http/src/main/java/io/helidon/http/ServerRequestHeaders.java
+++ b/http/http/src/main/java/io/helidon/http/ServerRequestHeaders.java
@@ -136,27 +136,30 @@ default Optional<MediaType> bestAccepted(MediaType... mediaTypes) {
         if (mediaTypes.length == 0) {
             return Optional.empty();
         }
-        List<HttpMediaType> accepted = acceptedTypes();
-        if (accepted.isEmpty()) {
-            return Optional.of(mediaTypes[0]);
-        }
-        double best = 0;
-        MediaType result = null;
-        for (MediaType mt : mediaTypes) {
-            for (HttpMediaType acc : accepted) {
-                double q = acc.qualityFactor();
-                if (q > best && acc.test(mt)) {
-                    if (q == 1) {
-                        return Optional.of(mt);
-                    } else {
-                        best = q;
-                        result = mt;
+        try {
+            List<HttpMediaType> accepted = acceptedTypes();
+            if (accepted.isEmpty()) {
+                return Optional.of(mediaTypes[0]);
+            }
+            double best = 0;
+            MediaType result = null;
+            for (MediaType mt : mediaTypes) {
+                for (HttpMediaType acc : accepted) {
+                    double q = acc.qualityFactor();
+                    if (q > best && acc.test(mt)) {
+                        if (q == 1) {
+                            return Optional.of(mt);
+                        } else {
+                            best = q;
+                            result = mt;
+                        }
                     }
                 }
             }
+            return Optional.ofNullable(result);
+        } catch (IllegalArgumentException e) {
+            throw new BadRequestException("Unable to parse Accept header", e);
         }
-
-        return Optional.ofNullable(result);
     }
 
     /**
diff --git a/http/http/src/main/java/io/helidon/http/ServerRequestHeadersImpl.java b/http/http/src/main/java/io/helidon/http/ServerRequestHeadersImpl.java
index 4570ebaca08..20b5d066645 100644
--- a/http/http/src/main/java/io/helidon/http/ServerRequestHeadersImpl.java
+++ b/http/http/src/main/java/io/helidon/http/ServerRequestHeadersImpl.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, 2023 Oracle and/or its affiliates.
+ * Copyright (c) 2022, 2024 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -82,13 +82,17 @@ public List<HttpMediaType> acceptedTypes() {
         } else {
             acceptedTypes = new ArrayList<>(5);
 
-            for (String acceptValue : acceptValues) {
-                List<String> tokenized = HeaderHelper.tokenize(',', acceptValue);
-                for (String token : tokenized) {
-                    acceptedTypes.add(HttpMediaType.create(token.trim()));
+            try {
+                for (String acceptValue : acceptValues) {
+                    List<String> tokenized = HeaderHelper.tokenize(',', acceptValue);
+                    for (String token : tokenized) {
+                        acceptedTypes.add(HttpMediaType.create(token.trim()));
+                    }
                 }
+                Collections.sort(acceptedTypes);
+            } catch (IllegalArgumentException e) {
+                throw new BadRequestException("Unable to parse Accept header", e);
             }
-            Collections.sort(acceptedTypes);
         }
         cachedAccepted = acceptedTypes;
 
diff --git a/webserver/observe/metrics/src/main/java/io/helidon/webserver/observe/metrics/MetricsFeature.java b/webserver/observe/metrics/src/main/java/io/helidon/webserver/observe/metrics/MetricsFeature.java
index 6ea0a52b410..453f6c1977e 100644
--- a/webserver/observe/metrics/src/main/java/io/helidon/webserver/observe/metrics/MetricsFeature.java
+++ b/webserver/observe/metrics/src/main/java/io/helidon/webserver/observe/metrics/MetricsFeature.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, 2023 Oracle and/or its affiliates.
+ * Copyright (c) 2022, 2024 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -186,6 +186,7 @@ private void getMatching(ServerRequest req,
         if (mediaType == null) {
             res.status(Status.NOT_ACCEPTABLE_406);
             res.send();
+            return;
         }
 
         getOrOptionsMatching(mediaType, res, () -> output(mediaType,
diff --git a/webserver/observe/metrics/src/test/java/io/helidon/webserver/observe/metrics/TestInvalidAcceptType.java b/webserver/observe/metrics/src/test/java/io/helidon/webserver/observe/metrics/TestInvalidAcceptType.java
new file mode 100644
index 00000000000..ae015af719f
--- /dev/null
+++ b/webserver/observe/metrics/src/test/java/io/helidon/webserver/observe/metrics/TestInvalidAcceptType.java
@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2024 Oracle and/or its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.helidon.webserver.observe.metrics;
+
+import java.util.List;
+
+import io.helidon.common.testing.http.junit5.SocketHttpClient;
+import io.helidon.http.Method;
+import io.helidon.webserver.http.HttpRouting;
+import io.helidon.webserver.testing.junit5.ServerTest;
+
+import io.helidon.webserver.testing.junit5.SetUpRoute;
+import jakarta.json.JsonObject;
+import org.junit.jupiter.api.Test;
+
+import static org.hamcrest.CoreMatchers.containsString;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+@ServerTest
+class TestInvalidAcceptType {
+
+    private final SocketHttpClient client;
+
+    @SetUpRoute
+    static void routing(HttpRouting.Builder router) {
+        router.post("/echo", (req, res) -> {
+            JsonObject message = req.content().as(JsonObject.class);
+            res.send(message);
+        });
+    }
+
+    TestInvalidAcceptType(SocketHttpClient client) {
+        this.client = client;
+    }
+
+    @Test
+    void checkResponseCode() {
+        String response = client.sendAndReceive(Method.POST,
+                "/echo",
+                "{ }",
+                List.of("Accept: application.json"));       // invalid media type
+        assertThat(response, containsString("400 Bad Request"));
+    }
+
+    @Test
+    void checkResponseCodeMetrics() {
+        String response = client.sendAndReceive(Method.GET,
+                "/observe/metrics",
+                null,
+                List.of("Accept: application.json"));       // invalid media type
+        assertThat(response, containsString("400 Bad Request"));
+    }
+}