diff --git a/compiler/src/dotty/tools/dotc/config/CommandLineParser.scala b/compiler/src/dotty/tools/dotc/config/CommandLineParser.scala
new file mode 100644
index 000000000000..2298b8b209cb
--- /dev/null
+++ b/compiler/src/dotty/tools/dotc/config/CommandLineParser.scala
@@ -0,0 +1,68 @@
+package dotty.tools.dotc
+package config
+
+import scala.annotation.tailrec
+import dotty.tools.sharable
+
+/** A simple (overly so) command line parser.
+ *  !!! This needs a thorough test suite to make sure quoting is
+ *  done correctly and portably.
+ */
+object CommandLineParser {
+  // splits a string into a quoted prefix and the rest of the string,
+  // taking escaping into account (using \)
+  // `"abc"def` will match as `DoubleQuoted(abc, def)`
+  private class QuotedExtractor(quote: Char) {
+    def unapply(in: String): Option[(String, String)] = {
+      val del = quote.toString
+      if (in startsWith del) {
+        var escaped = false
+        val (quoted, next) = (in substring 1) span {
+          case `quote` if !escaped => false
+          case '\\'    if !escaped => escaped = true; true
+          case _                   => escaped = false; true
+        }
+        // the only way to get out of the above loop is with an empty next or !escaped
+        // require(next.isEmpty || !escaped)
+        if (next startsWith del) Some((quoted, next substring 1))
+        else None
+      } else None
+    }
+  }
+  private object DoubleQuoted extends QuotedExtractor('"')
+  private object SingleQuoted extends QuotedExtractor('\'')
+  @sharable private val Word = """(\S+)(.*)""".r
+
+  // parse `in` for an argument, return it and the remainder of the input (or an error message)
+  // (argument may be in single/double quotes, taking escaping into account, quotes are stripped)
+  private def argument(in: String): Either[String, (String, String)] = in match {
+    case DoubleQuoted(arg, rest) => Right((arg, rest))
+    case SingleQuoted(arg, rest) => Right((arg, rest))
+    case Word(arg, rest)         => Right((arg, rest))
+    case _                       => Left(s"Illegal argument: $in")
+  }
+
+  // parse a list of whitespace-separated arguments (ignoring whitespace in quoted arguments)
+  @tailrec private def commandLine(in: String, accum: List[String] = Nil): Either[String, (List[String], String)] = {
+    val trimmed = in.trim
+    if (trimmed.isEmpty) Right((accum.reverse, ""))
+    else argument(trimmed) match {
+      case Right((arg, next)) =>
+        (next span Character.isWhitespace) match {
+          case("", rest) if rest.nonEmpty => Left("Arguments should be separated by whitespace.") // TODO: can this happen?
+          case(ws, rest)                  => commandLine(rest, arg :: accum)
+        }
+      case Left(msg) => Left(msg)
+    }
+  }
+
+  class ParseException(msg: String) extends RuntimeException(msg)
+
+  def tokenize(line: String): List[String] = tokenize(line, x => throw new ParseException(x))
+  def tokenize(line: String, errorFn: String => Unit): List[String] = {
+    commandLine(line) match {
+      case Right((args, _)) => args
+      case Left(msg)        => errorFn(msg) ; Nil
+    }
+  }
+}
diff --git a/compiler/src/dotty/tools/dotc/config/CompilerCommand.scala b/compiler/src/dotty/tools/dotc/config/CompilerCommand.scala
index ad6734675e98..6158c83c4958 100644
--- a/compiler/src/dotty/tools/dotc/config/CompilerCommand.scala
+++ b/compiler/src/dotty/tools/dotc/config/CompilerCommand.scala
@@ -1,7 +1,7 @@
 package dotty.tools.dotc
 package config
 
-import java.io.File
+import java.nio.file.{Files, Paths}
 import Settings._
 import core.Contexts._
 import util.DotClass
@@ -37,14 +37,18 @@ object CompilerCommand extends DotClass {
      * Expands all arguments starting with @ to the contents of the
      * file named like each argument.
      */
-    def expandArg(arg: String): List[String] = unsupported("expandArg")/*{
+    def expandArg(arg: String): List[String] = {
       def stripComment(s: String) = s takeWhile (_ != '#')
-      val file = File(arg stripPrefix "@")
-      if (!file.exists)
-        throw new java.io.FileNotFoundException("argument file %s could not be found" format file.name)
+      val path = Paths.get(arg stripPrefix "@")
+      if (!Files.exists(path))
+        throw new java.io.FileNotFoundException("argument file %s could not be found" format path.getFileName)
 
-      settings splitParams (file.lines() map stripComment mkString " ")
-    }*/
+      import scala.collection.JavaConversions._
+      val lines = Files.readAllLines(path) // default to UTF-8 encoding
+
+      val params = lines map stripComment mkString " "
+      CommandLineParser.tokenize(params)
+    }
 
     // expand out @filename to the contents of that filename
     def expandedArguments = args.toList flatMap {
diff --git a/compiler/test/dotty/tools/dotc/CompilationTests.scala b/compiler/test/dotty/tools/dotc/CompilationTests.scala
index a9d0d7e17718..20d5d61b3701 100644
--- a/compiler/test/dotty/tools/dotc/CompilationTests.scala
+++ b/compiler/test/dotty/tools/dotc/CompilationTests.scala
@@ -208,7 +208,8 @@ class CompilationTests extends ParallelTesting {
       defaultOutputDir + "lib/src/:" +
       // as well as bootstrapped compiler:
       defaultOutputDir + "dotty1/dotty/:" +
-      Jars.dottyInterfaces
+      Jars.dottyInterfaces,
+      "-Ycheck-reentrant"
     )
 
     def lib =