diff --git a/ethereumj-core/src/main/java/org/ethereum/vm/Program.java b/ethereumj-core/src/main/java/org/ethereum/vm/Program.java
index b91b906a..ad819db8 100644
--- a/ethereumj-core/src/main/java/org/ethereum/vm/Program.java
+++ b/ethereumj-core/src/main/java/org/ethereum/vm/Program.java
@@ -902,6 +902,9 @@ public class Program {
         OpCode op = OpCode.code(code[index]);
         final byte[] continuedCode;
 
+        if (op == null) throw new IllegalOperationException("Invalid operation: " +
+                        Hex.toHexString(code, index, 1));
+
         switch(op) {
             case PUSH1:  case PUSH2:  case PUSH3:  case PUSH4:  case PUSH5:  case PUSH6:  case PUSH7:  case PUSH8:
             case PUSH9:  case PUSH10: case PUSH11: case PUSH12: case PUSH13: case PUSH14: case PUSH15: case PUSH16:
@@ -975,7 +978,13 @@ public class Program {
     }
 
     @SuppressWarnings("serial")
-    public class IllegalOperationException extends RuntimeException {
+    public static class IllegalOperationException extends RuntimeException {
+        public IllegalOperationException(String message) {
+            super(message);
+        }
+
+        public IllegalOperationException() {
+        }
     }
 
     @SuppressWarnings("serial")
diff --git a/ethereumj-core/src/main/java/org/ethereum/vm/VM.java b/ethereumj-core/src/main/java/org/ethereum/vm/VM.java
index a41338d2..e1cb791a 100644
--- a/ethereumj-core/src/main/java/org/ethereum/vm/VM.java
+++ b/ethereumj-core/src/main/java/org/ethereum/vm/VM.java
@@ -80,7 +80,7 @@ public class VM {
         try {
             OpCode op = OpCode.code(program.getCurrentOp());
             if (op == null)
-                throw program.new IllegalOperationException();
+                throw new Program.IllegalOperationException();
 
             program.setLastOp(op.val());
             program.stackRequire(op.require());