diff --git a/src/main/scala/li/cil/oc/common/asm/ASMHelpers.java b/src/main/scala/li/cil/oc/common/asm/ASMHelpers.java
index ff4e044504..2d1e99afdb 100644
--- a/src/main/scala/li/cil/oc/common/asm/ASMHelpers.java
+++ b/src/main/scala/li/cil/oc/common/asm/ASMHelpers.java
@@ -122,7 +122,7 @@ public static void dumpClass(String className, byte[] originalBytes, byte[] tran
     }
   }
 
-  public static MethodNode copyMethodNode(MethodNode methodNode) {
+  public static synchronized MethodNode copyMethodNode(MethodNode methodNode) {
     MethodNode newMethodNode = new MethodNode(
       methodNode.access, methodNode.name, methodNode.desc, methodNode.signature,
       methodNode.exceptions == null ? null : methodNode.exceptions.toArray(new String[0])