diff --git a/src/main/java/moe/yushi/authlibinjector/AuthlibInjector.java b/src/main/java/moe/yushi/authlibinjector/AuthlibInjector.java
index 545e2bd..46a33b4 100644
--- a/src/main/java/moe/yushi/authlibinjector/AuthlibInjector.java
+++ b/src/main/java/moe/yushi/authlibinjector/AuthlibInjector.java
@@ -377,7 +377,7 @@ public final class AuthlibInjector {
 		Set<String> classNamesSet = new HashSet<>(Arrays.asList(classNames));
 		Class<?>[] classes = Stream.of(instrumentation.getAllLoadedClasses())
 				.filter(clazz -> classNamesSet.contains(clazz.getName()))
-				.filter(instrumentation::isModifiableClass)
+				.filter(AuthlibInjector::canRetransformClass)
 				.toArray(Class[]::new);
 		if (classes.length > 0) {
 			Logging.TRANSFORM.info("Attempt to retransform classes: " + Arrays.toString(classes));
@@ -389,6 +389,42 @@ public final class AuthlibInjector {
 		}
 	}
 
+	public static void retransformAllClasses() {
+		if (!retransformSupported) {
+			return;
+		}
+		Logging.TRANSFORM.info("Attempt to retransform all classes");
+		long t0 = System.currentTimeMillis();
+
+		Class<?>[] classes = Stream.of(instrumentation.getAllLoadedClasses())
+				.filter(AuthlibInjector::canRetransformClass)
+				.toArray(Class[]::new);
+		if (classes.length > 0) {
+			try {
+				instrumentation.retransformClasses(classes);
+			} catch (Throwable e) {
+				Logging.TRANSFORM.log(Level.WARNING, "Failed to retransform", e);
+				return;
+			}
+		}
+
+		long t1 = System.currentTimeMillis();
+		Logging.TRANSFORM.info("Retransformed " + classes.length + " classes in " + (t1 - t0) + "ms");
+	}
+
+	private static boolean canRetransformClass(Class<?> clazz) {
+		if (!instrumentation.isModifiableClass(clazz)) {
+			return false;
+		}
+		String name = clazz.getName();
+		for (String prefix : nonTransformablePackages) {
+			if (name.startsWith(prefix)) {
+				return false;
+			}
+		}
+		return true;
+	}
+
 	public static ClassTransformer getClassTransformer() {
 		return classTransformer;
 	}
diff --git a/src/main/java/moe/yushi/authlibinjector/javaagent/AuthlibInjectorPremain.java b/src/main/java/moe/yushi/authlibinjector/javaagent/AuthlibInjectorPremain.java
index 7327b9c..8086aa8 100644
--- a/src/main/java/moe/yushi/authlibinjector/javaagent/AuthlibInjectorPremain.java
+++ b/src/main/java/moe/yushi/authlibinjector/javaagent/AuthlibInjectorPremain.java
@@ -16,22 +16,15 @@
  */
 package moe.yushi.authlibinjector.javaagent;
 
-import static moe.yushi.authlibinjector.AuthlibInjector.PROP_API_ROOT;
-import static moe.yushi.authlibinjector.AuthlibInjector.bootstrap;
-import static moe.yushi.authlibinjector.AuthlibInjector.nonTransformablePackages;
 import java.lang.instrument.Instrumentation;
-import java.util.Arrays;
 import java.util.logging.Level;
 
+import moe.yushi.authlibinjector.AuthlibInjector;
 import moe.yushi.authlibinjector.InjectorInitializationException;
 import moe.yushi.authlibinjector.util.Logging;
 
 public class AuthlibInjectorPremain {
 
-	static {
-		Logging.init();
-	}
-
 	public static void premain(String arg, Instrumentation instrumentation) {
 		try {
 			initInjector(arg, instrumentation, false);
@@ -55,63 +48,18 @@ public class AuthlibInjectorPremain {
 		}
 	}
 
-	public static void initInjector(String arg, Instrumentation instrumentation, boolean needsRetransform) {
+	public static void initInjector(String arg, Instrumentation instrumentation, boolean retransform) {
 		setupConfig(arg);
+		AuthlibInjector.bootstrap(instrumentation);
 
-		boolean retransformSupported = instrumentation.isRetransformClassesSupported();
-		boolean retransformEnabled = retransformSupported && needsRetransform;
-		bootstrap(instrumentation);
-
-		if (needsRetransform) {
-			if (retransformSupported) {
-				Logging.TRANSFORM.info("Start retransforming");
-				doRetransform(instrumentation);
-			} else {
-				Logging.TRANSFORM.warning("Retransform is not supported");
-			}
+		if (retransform) {
+			AuthlibInjector.retransformAllClasses();
 		}
 	}
 
 	private static void setupConfig(String arg) {
 		if (arg != null && !arg.isEmpty()) {
-			System.setProperty(PROP_API_ROOT, arg);
+			System.setProperty(AuthlibInjector.PROP_API_ROOT, arg);
 		}
 	}
-
-	private static void doRetransform(Instrumentation instrumentation) {
-		try {
-			long t0 = System.currentTimeMillis();
-			Class<?>[] classToRetransform = getClassesToRetransform(instrumentation);
-			if (classToRetransform.length > 0) {
-				instrumentation.retransformClasses(classToRetransform);
-			}
-			long t1 = System.currentTimeMillis();
-			Logging.TRANSFORM.info("Retransform finished in " + (t1 - t0) + "ms");
-		} catch (Throwable e) {
-			Logging.TRANSFORM.log(Level.SEVERE, "Failed to retransform", e);
-		}
-	}
-
-	private static Class<?>[] getClassesToRetransform(Instrumentation instrumentation) {
-		Class<?>[] loadedClasses = instrumentation.getAllLoadedClasses();
-		Class<?>[] dest = new Class[loadedClasses.length];
-		int idx = 0;
-		for (Class<?> clazz : loadedClasses) {
-			if (instrumentation.isModifiableClass(clazz)) {
-				boolean toRetransform = true;
-				for (String nonTransformablePackage : nonTransformablePackages) {
-					if (clazz.getName().startsWith(nonTransformablePackage)) {
-						toRetransform = false;
-						break;
-					}
-				}
-				if (toRetransform) {
-					dest[idx++] = clazz;
-				}
-			}
-		}
-		Logging.TRANSFORM.fine("Loaded " + loadedClasses.length + " classes, " + idx + " to retransform");
-		return Arrays.copyOf(dest, idx);
-	}
-
 }
diff --git a/src/main/java/moe/yushi/authlibinjector/util/Logging.java b/src/main/java/moe/yushi/authlibinjector/util/Logging.java
index 856e297..3e0bc7e 100644
--- a/src/main/java/moe/yushi/authlibinjector/util/Logging.java
+++ b/src/main/java/moe/yushi/authlibinjector/util/Logging.java
@@ -43,9 +43,8 @@ public final class Logging {
 
 	private static Predicate<String> debugLoggerNamePredicate;
 
-	public static void init() {
+	static {
 		debugLoggerNamePredicate = createDebugLoggerNamePredicate();
-
 		initRootLogger();
 	}