diff --git a/README.md b/README.md
index cdce237ed..ff01a3052 100644
--- a/README.md
+++ b/README.md
@@ -52,8 +52,9 @@ Lastly, it can be used programmatically via its [API](#api) and has a Scala JS [
 4. [Limitations](#limitations)
 5. [FAQ](#faq)
 6. [Roadmap](#roadmap)
-7. [Contributors](#contributors)
-8. [Projects using coursier](#projects-using-coursier)
+7. [Development tips](#development-tips)
+8. [Contributors](#contributors)
+9. [Projects using coursier](#projects-using-coursier)
 
 ## Quick start
 
@@ -605,6 +606,17 @@ Set the `COURSIER_NO_TERM` environment variable to `1`. This disables the
 progress bar message, and prints simple `Downloading URL` / `Downloaded URL`
 instead.
 
+## Development tips
+
+#### Working on the plugin module in an IDE
+
+Set `scalaVersion` to `2.10.6` in `build.sbt`. Then re-open / reload the coursier project.
+
+#### Running the Scala JS tests
+
+They require `npm install` to have been run once from the `coursier` directory or a subdirectory of
+it. They can then be run with `sbt testsJS/test`.
+
 ## Roadmap
 
 The first releases were milestones like `0.1.0-M?`. As a launcher, basic Ivy
diff --git a/doc/README.md b/doc/README.md
index dc45347da..dac98922e 100644
--- a/doc/README.md
+++ b/doc/README.md
@@ -52,8 +52,9 @@ Lastly, it can be used programmatically via its [API](#api) and has a Scala JS [
 4. [Limitations](#limitations)
 5. [FAQ](#faq)
 6. [Roadmap](#roadmap)
-7. [Contributors](#contributors)
-8. [Projects using coursier](#projects-using-coursier)
+7. [Development tips](#development-tips)
+8. [Contributors](#contributors)
+9. [Projects using coursier](#projects-using-coursier)
 
 ## Quick start
 
@@ -629,6 +630,17 @@ Set the `COURSIER_NO_TERM` environment variable to `1`. This disables the
 progress bar message, and prints simple `Downloading URL` / `Downloaded URL`
 instead.
 
+## Development tips
+
+#### Working on the plugin module in an IDE
+
+Set `scalaVersion` to `2.10.6` in `build.sbt`. Then re-open / reload the coursier project.
+
+#### Running the Scala JS tests
+
+They require `npm install` to have been run once from the `coursier` directory or a subdirectory of
+it. They can then be run with `sbt testsJS/test`.
+
 ## Roadmap
 
 The first releases were milestones like `0.1.0-M?`. As a launcher, basic Ivy
diff --git a/plugin/src/main/scala-2.10/coursier/Tasks.scala b/plugin/src/main/scala-2.10/coursier/Tasks.scala
index 96582b6fd..b88058e75 100644
--- a/plugin/src/main/scala-2.10/coursier/Tasks.scala
+++ b/plugin/src/main/scala-2.10/coursier/Tasks.scala
@@ -154,6 +154,14 @@ object Tasks {
 
   private val resolutionsCache = new mutable.HashMap[CacheKey, UpdateReport]
 
+  private def forcedScalaModules(scalaVersion: String): Map[Module, String] =
+    Map(
+      Module("org.scala-lang", "scala-library") -> scalaVersion,
+      Module("org.scala-lang", "scala-compiler") -> scalaVersion,
+      Module("org.scala-lang", "scala-reflect") -> scalaVersion,
+      Module("org.scala-lang", "scalap") -> scalaVersion
+    )
+
   def updateTask(withClassifiers: Boolean, sbtClassifiers: Boolean = false) = Def.task {
 
     // SBT logging should be better than that most of the time...
@@ -209,6 +217,8 @@ object Tasks {
       val cachePolicy = coursierCachePolicy.value
       val cacheDir = coursierCache.value
 
+      val sv = scalaVersion.value // is this always defined? (e.g. for Java only projects?)
+
       val resolvers =
         if (sbtClassifiers)
           coursierSbtResolvers.value
@@ -221,7 +231,7 @@ object Tasks {
       val startRes = Resolution(
         currentProject.dependencies.map { case (_, dep) => dep }.toSet,
         filter = Some(dep => !dep.optional),
-        forceVersions = projects.map(_.moduleVersion).toMap
+        forceVersions = forcedScalaModules(sv) ++ projects.map(_.moduleVersion)
       )
 
       // required for publish to be fine, later on
diff --git a/tests/js/src/test/scala/coursier/test/compatibility/package.scala b/tests/js/src/test/scala/coursier/test/compatibility/package.scala
index fb2d0da9c..c9c7d11fa 100644
--- a/tests/js/src/test/scala/coursier/test/compatibility/package.scala
+++ b/tests/js/src/test/scala/coursier/test/compatibility/package.scala
@@ -15,7 +15,7 @@ package object compatibility {
 
     fs.readFile("tests/shared/src/test/resources/" + path, "utf-8", {
       (err: js.Dynamic, data: js.Dynamic) =>
-        if (err == null) p.success(data.asInstanceOf[String])
+        if (js.isUndefined(err) || err == null) p.success(data.asInstanceOf[String])
         else p.failure(new Exception(err.toString))
         ()
     }: js.Function2[js.Dynamic, js.Dynamic, Unit])