diff --git a/pitest/src/main/java/org/pitest/coverage/execute/CoverageMinion.java b/pitest/src/main/java/org/pitest/coverage/execute/CoverageMinion.java
index f86dd7177..b043e5318 100644
--- a/pitest/src/main/java/org/pitest/coverage/execute/CoverageMinion.java
+++ b/pitest/src/main/java/org/pitest/coverage/execute/CoverageMinion.java
@@ -34,6 +34,7 @@
 
 import java.io.BufferedOutputStream;
 import java.io.IOException;
+import java.lang.instrument.ClassFileTransformer;
 import java.net.Socket;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -123,7 +124,10 @@ public static void main(final String[] args) {
   private static void enableTransformations() {
     ClientPluginServices plugins = ClientPluginServices.makeForContextLoader();
     for (TransformationPlugin each : plugins.findTransformations()) {
-      HotSwapAgent.addTransformer(each.makeCoverageTransformer());
+      ClassFileTransformer transformer = each.makeCoverageTransformer();
+      if (transformer != null) {
+        HotSwapAgent.addTransformer(transformer);
+      }
     }
   }
 
diff --git a/pitest/src/main/java/org/pitest/mutationtest/environment/TransformationPlugin.java b/pitest/src/main/java/org/pitest/mutationtest/environment/TransformationPlugin.java
index 0b172cbdd..9de0c0a1c 100644
--- a/pitest/src/main/java/org/pitest/mutationtest/environment/TransformationPlugin.java
+++ b/pitest/src/main/java/org/pitest/mutationtest/environment/TransformationPlugin.java
@@ -5,7 +5,18 @@
 import java.lang.instrument.ClassFileTransformer;
 
 public interface TransformationPlugin extends ClientClasspathPlugin {
-    ClassFileTransformer makeCoverageTransformer();
-    ClassFileTransformer makeMutationTransformer();
+
+    @Deprecated
+    default ClassFileTransformer makeTransformer() {
+        return makeMutationTransformer();
+    }
+
+    default ClassFileTransformer makeCoverageTransformer() {
+        return null;
+    }
+
+    default ClassFileTransformer makeMutationTransformer() {
+        return null;
+    }
 
 }
diff --git a/pitest/src/main/java/org/pitest/mutationtest/execute/MutationTestMinion.java b/pitest/src/main/java/org/pitest/mutationtest/execute/MutationTestMinion.java
index 80ea4189f..17908aa34 100644
--- a/pitest/src/main/java/org/pitest/mutationtest/execute/MutationTestMinion.java
+++ b/pitest/src/main/java/org/pitest/mutationtest/execute/MutationTestMinion.java
@@ -37,6 +37,7 @@
 import javax.management.NotificationListener;
 import javax.management.openmbean.CompositeData;
 import java.io.IOException;
+import java.lang.instrument.ClassFileTransformer;
 import java.lang.management.MemoryNotificationInfo;
 import java.net.Socket;
 import java.util.Collection;
@@ -169,7 +170,10 @@ private static List<TestUnit> findTestsForTestClasses(
   private static void enableTransformations() {
     ClientPluginServices plugins = ClientPluginServices.makeForContextLoader();
     for (TransformationPlugin each : plugins.findTransformations()) {
-      HotSwapAgent.addTransformer(each.makeMutationTransformer());
+      ClassFileTransformer transformer = each.makeMutationTransformer();
+      if (transformer != null) {
+        HotSwapAgent.addTransformer(transformer);
+      }
     }
   }
 
diff --git a/pitest/src/main/java/org/pitest/mutationtest/mocksupport/JavassistCoverageInterceptor.java b/pitest/src/main/java/org/pitest/mutationtest/mocksupport/JavassistCoverageInterceptor.java
index afb4accc2..6e2da7b27 100644
--- a/pitest/src/main/java/org/pitest/mutationtest/mocksupport/JavassistCoverageInterceptor.java
+++ b/pitest/src/main/java/org/pitest/mutationtest/mocksupport/JavassistCoverageInterceptor.java
@@ -115,8 +115,12 @@ private static InputStream returnNormalBytes(final Object classPath,
     // so the best we can do is exclude pitest itself and some common classes.
     private static Predicate<String> excluded() {
       return Prelude.or(
+              startsWith("org.objenesis."),
+              startsWith("net.bytebuddy."),
               startsWith("javassist."),
               startsWith("org.pitest."),
+              startsWith("com.groupcdg."),
+              startsWith("com.arcmutate."),
               startsWith("java."),
               startsWith("javax."),
               startsWith("com.sun."),