diff --git a/src/main/scala/tilelink/ErrorEvaluator.scala b/src/main/scala/tilelink/ErrorEvaluator.scala
index 2a1bdb4b..1bcd71a0 100644
--- a/src/main/scala/tilelink/ErrorEvaluator.scala
+++ b/src/main/scala/tilelink/ErrorEvaluator.scala
@@ -7,34 +7,50 @@ import freechips.rocketchip.config.Parameters
 import freechips.rocketchip.diplomacy._
 import freechips.rocketchip.util._
 
+// Check if a request satisfies some interesting property
+class RequestPattern(test: TLBundleA => Bool)
+{
+  def apply(a: TLBundleA) = test(a)
+}
+
+object RequestPattern
+{
+  // Does the request address range overlap a particular pattern of addresses?
+  def overlaps(pattern: Seq[AddressSet])(a: TLBundleA) = {
+    val amask = UIntToOH1(a.size, a.params.addressBits)
+    val abase = a.address
+    pattern.map { case p =>
+      val pbase = UInt(p.base)
+      val pmask = UInt(p.mask & ((BigInt(1) << a.params.addressBits) - 1))
+      (amask | pmask | ~(abase ^ pbase)).andR
+    }.reduce(_ || _)
+  }
+
+  implicit def apply(pattern: Seq[AddressSet]): RequestPattern = new RequestPattern(overlaps(pattern) _)
+}
+
 // An ErrorEvaluator is used for test harnesses.
-// It creates errors in transactions which overlap an address in pattern.
+// It creates errors in transactions which match the provided test function.
 // If testOn is true, it will assert fail if these transactions do not already error.
 // If testOff is true, it will assert fail if these transactions otherwise error.
 // This helps when building unit tests to confirm that errors are propagated correctly.
-class TLErrorEvaluator(pattern: Seq[AddressSet], testOn: Boolean, testOff: Boolean)(implicit p: Parameters) extends LazyModule
+class TLErrorEvaluator(test: RequestPattern, testOn: Boolean, testOff: Boolean)(implicit p: Parameters) extends LazyModule
 {
   val node = TLAdapterNode()
   lazy val module = new LazyModuleImp(this) {
     (node.in zip node.out) foreach { case ((in, edgeIn), (out, edgeOut)) =>
       out <> in
 
-      // Does the request overlap the pattern ?
-      val abase = in.a.bits.address
-      val amask = UIntToOH1(in.a.bits.size, log2Up(edgeIn.maxTransfer))
-      val overlaps = pattern.map { case a =>
-        val pbase = UInt(a.base)
-        val pmask = UInt(a.mask & ((BigInt(1) << edgeIn.bundle.addressBits) - 1))
-        (amask | pmask | ~(abase ^ pbase)).andR
-      }.reduce(_ || _)
+      // Should the request receive an error ?
+      val inject_map = Mem(edgeIn.client.endSourceId, Bool())
+      val inject_now = test(in.a.bits)
 
       val (d_first, d_last, _) = edgeOut.firstlast(out.d)
 
-      val inject = Mem(edgeIn.client.endSourceId, Bool())
-      when (in.a.fire()) { inject.write(in.a.bits.source, overlaps) }
+      when (in.a.fire()) { inject_map.write(in.a.bits.source, inject_now) }
 
       val bypass = in.a.fire() && in.a.bits.source === in.d.bits.source
-      val d_inject = Mux(bypass, overlaps, inject.read(in.d.bits.source)) holdUnless d_first
+      val d_inject = Mux(bypass, inject_now, inject_map.read(in.d.bits.source)) holdUnless d_first
       in.d.bits.error := out.d.bits.error || (d_last && d_inject)
 
       assert (Bool(!testOn)  || !out.d.fire() || !d_last || !d_inject ||  out.d.bits.error, "Error flag was not set!")
@@ -45,6 +61,6 @@ class TLErrorEvaluator(pattern: Seq[AddressSet], testOn: Boolean, testOff: Boole
 
 object TLErrorEvaluator
 {
-  def apply(pattern: Seq[AddressSet], testOn: Boolean = false, testOff: Boolean = false)(implicit p: Parameters): TLNode =
-    LazyModule(new TLErrorEvaluator(pattern, testOn, testOff)).node
+  def apply(test: RequestPattern, testOn: Boolean = false, testOff: Boolean = false)(implicit p: Parameters): TLNode =
+    LazyModule(new TLErrorEvaluator(test, testOn, testOff)).node
 }