diff --git a/src/main/scala/vexriscv/Services.scala b/src/main/scala/vexriscv/Services.scala
index 64ce5ae..8a291d6 100644
--- a/src/main/scala/vexriscv/Services.scala
+++ b/src/main/scala/vexriscv/Services.scala
@@ -24,6 +24,7 @@ trait DecoderService{
   def add(key : MaskedLiteral,values : Seq[(Stageable[_ <: BaseType],Any)])
   def add(encoding :Seq[(MaskedLiteral,Seq[(Stageable[_ <: BaseType],Any)])])
   def addDefault(key : Stageable[_ <: BaseType], value : Any)
+  def forceIllegal() : Unit
 }
 
 case class ExceptionCause(codeWidth : Int) extends Bundle{
diff --git a/src/main/scala/vexriscv/plugin/DecoderSimplePlugin.scala b/src/main/scala/vexriscv/plugin/DecoderSimplePlugin.scala
index 71e3894..a2ab111 100644
--- a/src/main/scala/vexriscv/plugin/DecoderSimplePlugin.scala
+++ b/src/main/scala/vexriscv/plugin/DecoderSimplePlugin.scala
@@ -71,6 +71,8 @@ class DecoderSimplePlugin(catchIllegalInstruction : Boolean = false,
     }
   }
 
+  def forceIllegal() : Unit = if(catchIllegalInstruction) pipeline.decode.input(pipeline.config.LEGAL_INSTRUCTION) := False
+
   val defaults = mutable.LinkedHashMap[Stageable[_ <: BaseType], BaseType]()
   val encodings = mutable.LinkedHashMap[MaskedLiteral,ArrayBuffer[(Stageable[_ <: BaseType], BaseType)]]()
   var decodeExceptionPort : Flow[ExceptionCause] = null