diff --git a/.github/workflows/maven.yml b/.github/workflows/maven.yml
index c0342d7478..3219d051d2 100644
--- a/.github/workflows/maven.yml
+++ b/.github/workflows/maven.yml
@@ -49,4 +49,4 @@ jobs:
         distribution: 'temurin'
         java-version: ${{ matrix.java }}
     - name: Build with Maven
-      run: ./mvnw -V --file pom.xml --no-transfer-progress -DtrimStackTrace=false -P-use-toolchains,docker
+      run: ./mvnw -V --file pom.xml --no-transfer-progress -DtrimStackTrace=false -Djunit.jupiter.execution.parallel.enabled=false -P-use-toolchains,docker
diff --git a/httpcore5-testing/pom.xml b/httpcore5-testing/pom.xml
index 92fc1a6b20..2aad7462e5 100644
--- a/httpcore5-testing/pom.xml
+++ b/httpcore5-testing/pom.xml
@@ -90,6 +90,11 @@
       <artifactId>junit-jupiter</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.junit.platform</groupId>
+      <artifactId>junit-platform-launcher</artifactId>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>org.hamcrest</groupId>
       <artifactId>hamcrest</artifactId>
@@ -205,4 +210,4 @@
     </plugins>
   </reporting>
 
-</project>
\ No newline at end of file
+</project>
diff --git a/httpcore5-testing/src/test/java/org/apache/hc/core5/testing/LoggingInitializationListener.java b/httpcore5-testing/src/test/java/org/apache/hc/core5/testing/LoggingInitializationListener.java
new file mode 100644
index 0000000000..0152385ad3
--- /dev/null
+++ b/httpcore5-testing/src/test/java/org/apache/hc/core5/testing/LoggingInitializationListener.java
@@ -0,0 +1,42 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package org.apache.hc.core5.testing;
+
+import org.junit.platform.launcher.LauncherSession;
+import org.junit.platform.launcher.LauncherSessionListener;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Initialize Slf4j centrally before any tests run. This prevents Slf4j from
+ * spamming warnings during parallelized test runs.
+ */
+public class LoggingInitializationListener implements LauncherSessionListener {
+    @Override
+    public void launcherSessionOpened(final LauncherSession session) {
+        LoggerFactory.getILoggerFactory();
+    }
+}
diff --git a/httpcore5-testing/src/test/java/org/apache/hc/core5/testing/nio/AlpnTests.java b/httpcore5-testing/src/test/java/org/apache/hc/core5/testing/nio/AlpnTests.java
index 4bcae56d9b..5005a99aa4 100644
--- a/httpcore5-testing/src/test/java/org/apache/hc/core5/testing/nio/AlpnTests.java
+++ b/httpcore5-testing/src/test/java/org/apache/hc/core5/testing/nio/AlpnTests.java
@@ -37,10 +37,12 @@
 import org.junit.jupiter.api.condition.EnabledForJreRange;
 import org.junit.jupiter.api.condition.JRE;
 import org.junit.jupiter.api.condition.OS;
+import org.junit.jupiter.api.parallel.Isolated;
 
 class AlpnTests {
 
     @Nested
+    @Isolated
     @DisplayName("ALPN Oracle")
     class OracleJSSEAlpnTest extends AlpnTest {
 
@@ -51,6 +53,7 @@ public OracleJSSEAlpnTest() throws Exception {
     }
 
     @Nested
+    @Isolated
     @DisplayName("ALPN Conscrypt (Java 9 or newer)")
     @DisabledOnOs(OS.MAC)
     @EnabledForJreRange(min = JRE.JAVA_9)
@@ -63,6 +66,7 @@ public ConscryptJSSEAlpnTest() throws Exception {
     }
 
     @Nested
+    @Isolated
     @DisplayName("ALPN Conscrypt (Conscrypt specific TLS strategies)")
     @DisabledOnOs(OS.MAC)
     class ConscryptJSSEAndStrategiesAlpnTest extends AlpnTest {
diff --git a/httpcore5-testing/src/test/resources/META-INF/services/org.junit.platform.launcher.LauncherSessionListener b/httpcore5-testing/src/test/resources/META-INF/services/org.junit.platform.launcher.LauncherSessionListener
new file mode 100644
index 0000000000..0cd9f6efc3
--- /dev/null
+++ b/httpcore5-testing/src/test/resources/META-INF/services/org.junit.platform.launcher.LauncherSessionListener
@@ -0,0 +1,19 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+#
+org.apache.hc.core5.testing.LoggingInitializationListener
diff --git a/httpcore5/src/test/java/org/apache/hc/core5/ssl/TestSSLContextBuilder.java b/httpcore5/src/test/java/org/apache/hc/core5/ssl/TestSSLContextBuilder.java
index 81ac48c282..16539124dc 100644
--- a/httpcore5/src/test/java/org/apache/hc/core5/ssl/TestSSLContextBuilder.java
+++ b/httpcore5/src/test/java/org/apache/hc/core5/ssl/TestSSLContextBuilder.java
@@ -66,10 +66,12 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.Isolated;
 
 /**
  * Unit tests for {@link SSLContextBuilder}.
  */
+@Isolated
 class TestSSLContextBuilder {
 
     static final String PROVIDER_SUN_JSSE = "SunJSSE";
diff --git a/httpcore5/src/test/resources/junit-platform.properties b/httpcore5/src/test/resources/junit-platform.properties
new file mode 100644
index 0000000000..25e8e686d6
--- /dev/null
+++ b/httpcore5/src/test/resources/junit-platform.properties
@@ -0,0 +1,22 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+#
+junit.jupiter.execution.parallel.enabled = true
+junit.jupiter.execution.parallel.mode.default = concurrent
+junit.jupiter.execution.parallel.mode.classes.default = concurrent
+junit.jupiter.execution.parallel.config.strategy = dynamic