diff --git a/core/src/main/java/hudson/PluginFirstClassLoader.java b/core/src/main/java/hudson/PluginFirstClassLoader.java
index 51df9e462501..8aee057e7b39 100644
--- a/core/src/main/java/hudson/PluginFirstClassLoader.java
+++ b/core/src/main/java/hudson/PluginFirstClassLoader.java
@@ -42,10 +42,6 @@
 public class PluginFirstClassLoader
     extends AntClassLoader
 {
-    static {
-        registerAsParallelCapable();
-    }
-
     public PluginFirstClassLoader() {
         super(null, false);
     }
diff --git a/core/src/main/java/jenkins/util/AntClassLoader.java b/core/src/main/java/jenkins/util/AntClassLoader.java
index b5326743768e..28b0dea743b2 100644
--- a/core/src/main/java/jenkins/util/AntClassLoader.java
+++ b/core/src/main/java/jenkins/util/AntClassLoader.java
@@ -92,7 +92,6 @@ public class AntClassLoader extends ClassLoader implements JenkinsClassLoader, S
     private static final Object MR_JARFILE_CTOR_RUNTIME_VERSION_VAL;
 
     static {
-        registerAsParallelCapable();
         if (IS_ATLEAST_JAVA9) {
             Class[] ctorArgs = null;
             Object runtimeVersionVal = null;