diff --git a/check/src/main/scala/rsc/checkscalasig/Checker.scala b/check/src/main/scala/rsc/checkscalasig/Checker.scala
index dce2c974..a88a98f1 100644
--- a/check/src/main/scala/rsc/checkscalasig/Checker.scala
+++ b/check/src/main/scala/rsc/checkscalasig/Checker.scala
@@ -4,7 +4,7 @@ import better.files._
 import java.nio.file.Path
 import rsc.checkbase.{CheckerBase, DiffUtil, DifferentProblem}
 import scala.collection.mutable
-import scala.meta.scalasig.highlevel.{ParsedScalasig, ScalasigResult, Scalasigs}
+import scala.meta.scalasig.highlevel._
 
 /**
  *
@@ -21,16 +21,20 @@ class Checker(settings: Settings, nscResult: Path, rscResult: Path)
   val nscFilenameDefaultBase = "nsc_scalasigs"
   val rscFilenameDefaultBase = "rsc_scalasigs"
 
-  private def resStr(sig: ScalasigResult): Option[(String, String)] = {
+  private def symbols(scalasig: Scalasig): Map[Id, EmbeddedSymbol] =
+    scalasig.symbols.map(sym => sym.id -> sym).toMap
+
+  private def resultSyms(sig: ScalasigResult): Option[(String, Map[Id, EmbeddedSymbol])] = {
     sig match {
-      case ParsedScalasig(_, _, scalasig) => Some(scalasig.name -> scalasig.toString)
+      case ParsedScalasig(_, _, scalasig) => Some(scalasig.name -> symbols(scalasig))
       case _ => None
     }
   }
 
   def check(): Unit = {
-    val nscSigs = Scalasigs.list(nscResult).flatMap(resStr).toMap
-    val rscSigs = Scalasigs.list(rscResult).flatMap(resStr).toMap
+
+    val nscSigs = Scalasigs.list(nscResult).flatMap(resultSyms).toMap
+    val rscSigs = Scalasigs.list(rscResult).flatMap(resultSyms).toMap
 
     assert(nscSigs.keySet == rscSigs.keySet)
 
@@ -38,18 +42,26 @@ class Checker(settings: Settings, nscResult: Path, rscResult: Path)
     val rscTexts = mutable.ListBuffer.empty[String]
 
     nscSigs.foreach {
-      case (k, nscText) =>
-        val rscText = rscSigs(k)
+      case (k, nscSyms) =>
+        val rscSyms = rscSigs(k)
+
+        val nscSymStrs = nscSyms.mapValues(_.toString)
+        val rscSymStrs = rscSyms.mapValues(_.toString)
 
         if (settings.saveOutput) {
-          nscTexts.prepend(nscText)
-          rscTexts.prepend(rscText)
+          nscTexts.prepend(nscSymStrs.mkString("\n"))
+          rscTexts.prepend(rscSymStrs.mkString("\n"))
         }
 
-        val unifiedDiff = diff(nscResult.toString, nscText, rscText.toString, rscText)
+        val relevant_ids = (nscSymStrs.keySet ++ rscSymStrs.keySet).toList.sorted
+
+        relevant_ids.foreach { id =>
+          val nscString = nscSymStrs.getOrElse(id, "")
+          val rscString = rscSymStrs.getOrElse(id, "")
 
-        unifiedDiff.foreach { d =>
-          problems += DifferentProblem(d)
+          if (nscString != rscString) {
+            problems += DifferentProblem(s"$k: $id", nscString, rscString)
+          }
         }
     }
 
diff --git a/check/src/main/scala/rsc/checkscalasig/Main.scala b/check/src/main/scala/rsc/checkscalasig/Main.scala
index 1d8e9889..5b44d785 100644
--- a/check/src/main/scala/rsc/checkscalasig/Main.scala
+++ b/check/src/main/scala/rsc/checkscalasig/Main.scala
@@ -8,6 +8,10 @@ import _root_.rsc.checkbase.{SimpleBase, ToolResult}
  * check/runMain rsc.checkscalasig.Main --classpath $JAVALIB:SCALALIB C.scala
  *
  * Replace $JAVALIB:SCALALIB with the actual paths
+ *
+ * Or in --classfiles mode to check output
+ *
+ * check/runMain rsc.checkscalasig.Main --classfiles rsc_output.jar nsc_output.jar
  */
 object Main extends SimpleBase[Settings, Path, Path] {
 
@@ -16,11 +20,11 @@ object Main extends SimpleBase[Settings, Path, Path] {
   }
 
   def nscResult(settings: Settings): ToolResult[Path] = {
-    nsc(settings.cp, settings.ins)
+    settings.classfiles.nsc.map(Right(_)).getOrElse(nsc(settings.cp, settings.ins))
   }
 
   def rscResult(settings: Settings): ToolResult[Path] = {
-    rsc(settings.cp, settings.ins)
+    settings.classfiles.rsc.map(Right(_)).getOrElse(rsc(settings.cp, settings.ins))
   }
 
   def checker(settings: Settings, nscResult: Path, rscResult: Path): Checker = {
diff --git a/check/src/main/scala/rsc/checkscalasig/Settings.scala b/check/src/main/scala/rsc/checkscalasig/Settings.scala
index 1c9418a8..0ff60e37 100644
--- a/check/src/main/scala/rsc/checkscalasig/Settings.scala
+++ b/check/src/main/scala/rsc/checkscalasig/Settings.scala
@@ -3,15 +3,23 @@ package rsc.checkscalasig
 import java.io.File.pathSeparator
 import java.nio.file.{Path, Paths}
 import rsc.checkbase.SettingsBase
+import rsc.checkscalasig.Settings.ClassfilesPath
 
 final case class Settings(
     cp: List[Path] = Nil,
     ins: List[Path] = Nil,
     quiet: Boolean = false,
-    saveOutput: Boolean = false
+    saveOutput: Boolean = false,
+    classfiles: ClassfilesPath = ClassfilesPath(None, None)
 ) extends SettingsBase
 
 object Settings {
+
+  final case class ClassfilesPath(rsc: Option[Path], nsc: Option[Path])
+
+  private def pathsFor(pathStr: String): List[Path] =
+    pathStr.split(pathSeparator).map(s => Paths.get(s)).toList
+
   def parse(args: List[String]): Either[List[String], Settings] = {
     def loop(
         settings: Settings,
@@ -20,8 +28,15 @@ object Settings {
       args match {
         case "--" +: rest =>
           loop(settings, false, rest)
+        case "--classfiles" +: rsc_path +: nsc_path +: Nil =>
+          val rsc_files = Paths.get(rsc_path)
+          val nsc_files = Paths.get(nsc_path)
+          loop(
+            settings.copy(classfiles = ClassfilesPath(Some(rsc_files), Some(nsc_files))),
+            true,
+            Nil)
         case "--classpath" +: s_cp +: rest if allowOptions =>
-          val cp = s_cp.split(pathSeparator).map(s => Paths.get(s)).toList
+          val cp = pathsFor(s_cp)
           loop(settings.copy(cp = settings.cp ++ cp), true, rest)
         case "--save-output" +: rest if allowOptions =>
           loop(settings.copy(saveOutput = true), true, rest)