diff --git a/src/main/java/de/malkusch/km200/KM200.java b/src/main/java/de/malkusch/km200/KM200.java
index 261d479..345747d 100644
--- a/src/main/java/de/malkusch/km200/KM200.java
+++ b/src/main/java/de/malkusch/km200/KM200.java
@@ -17,6 +17,7 @@
 import de.malkusch.km200.http.Http;
 import de.malkusch.km200.http.JdkHttp;
 import de.malkusch.km200.http.RetryHttp;
+import de.malkusch.km200.http.SerializedHttp;
 
 /**
  * This is an API for Bosch/Buderus/Junkers heaters with a KM200 gateway.
@@ -126,9 +127,17 @@ public KM200(String uri, int retries, Duration timeout, String gatewayPassword,
         this.comm = new KM200Comm();
 
         {
-            var jdkHttp = new JdkHttp(uri.replaceAll("/*$", ""), USER_AGENT, timeout);
-            queryHttp = new RetryHttp(jdkHttp, retries, IOException.class, ServerError.class);
-            updateHttp = new RetryHttp(jdkHttp, retries, ServerError.class);
+            Http http = new JdkHttp(uri.replaceAll("/*$", ""), USER_AGENT, timeout);
+
+            /*
+             * The KM200 itself is not thread safe. This proxy serializes all
+             * requests to protect users from a wrong concurrent usage of this
+             * API.
+             */
+            http = new SerializedHttp(http);
+
+            queryHttp = new RetryHttp(http, retries, IOException.class, ServerError.class);
+            updateHttp = new RetryHttp(http, retries, ServerError.class);
         }
 
         query("/system");
diff --git a/src/main/java/de/malkusch/km200/http/JdkHttp.java b/src/main/java/de/malkusch/km200/http/JdkHttp.java
index 6180c78..a2189ec 100644
--- a/src/main/java/de/malkusch/km200/http/JdkHttp.java
+++ b/src/main/java/de/malkusch/km200/http/JdkHttp.java
@@ -45,30 +45,22 @@ public Response post(String path, byte[] body) throws IOException, InterruptedEx
         return send(request);
     }
 
-    private final Object serializedSendLock = new Object();
-
     private Response send(HttpRequest request) throws IOException, InterruptedException, KM200Exception {
-        /*
-         * The KM200 itself is not thread safe. This lock serializes all
-         * requests to protect users from a wrong concurrent usage of this API.
-         */
-        synchronized (serializedSendLock) {
-            var response = client.send(request, BodyHandlers.ofByteArray());
-            var status = response.statusCode();
+        var response = client.send(request, BodyHandlers.ofByteArray());
+        var status = response.statusCode();
 
-            if (status >= 200 && status <= 299) {
-                return new Response(status, response.body());
+        if (status >= 200 && status <= 299) {
+            return new Response(status, response.body());
 
-            } else {
-                throw switch (status) {
-                case 400 -> new KM200Exception.BadRequest("Bad request to " + request.uri());
-                case 403 -> new KM200Exception.Forbidden(request.uri() + " is forbidden");
-                case 404 -> new KM200Exception.NotFound(request.uri() + " was not found");
-                case 423 -> new KM200Exception.Locked(request.uri() + " was locked");
-                case 500 -> new KM200Exception.ServerError(request.uri() + " resulted in a server error");
-                default -> new KM200Exception(request.uri() + " failed with response code " + status);
-                };
-            }
+        } else {
+            throw switch (status) {
+            case 400 -> new KM200Exception.BadRequest("Bad request to " + request.uri());
+            case 403 -> new KM200Exception.Forbidden(request.uri() + " is forbidden");
+            case 404 -> new KM200Exception.NotFound(request.uri() + " was not found");
+            case 423 -> new KM200Exception.Locked(request.uri() + " was locked");
+            case 500 -> new KM200Exception.ServerError(request.uri() + " resulted in a server error");
+            default -> new KM200Exception(request.uri() + " failed with response code " + status);
+            };
         }
     }
 
diff --git a/src/main/java/de/malkusch/km200/http/SerializedHttp.java b/src/main/java/de/malkusch/km200/http/SerializedHttp.java
new file mode 100644
index 0000000..99e7555
--- /dev/null
+++ b/src/main/java/de/malkusch/km200/http/SerializedHttp.java
@@ -0,0 +1,30 @@
+package de.malkusch.km200.http;
+
+import java.io.IOException;
+
+import de.malkusch.km200.KM200Exception;
+
+public final class SerializedHttp implements Http {
+
+    private final Http http;
+
+    public SerializedHttp(Http http) {
+        this.http = http;
+    }
+
+    private final Object lock = new Object();
+
+    @Override
+    public Response get(String path) throws IOException, InterruptedException, KM200Exception {
+        synchronized (lock) {
+            return http.get(path);
+        }
+    }
+
+    @Override
+    public Response post(String path, byte[] body) throws IOException, InterruptedException, KM200Exception {
+        synchronized (lock) {
+            return http.post(path, body);
+        }
+    }
+}