How to reference external sbt project from another sbt project?

I have the following setup of a Scala application and a common core library: root

 -> /ApplicationA
   -> /project
     -> /build.sbt
 -> /CoreLibrary
   -> /project
     -> /build.sbt

I want to add a reference from ApplicationA to CoreLibrary à la Eclipse project reference, so that every time CoreLibrary changes ApplicationA is built as well. I´ve tried the following contents of build.Scala for ApplicationA:

  val core = Project(
      id = "platform-core",
      base = file("../CoreLibrary"))

  val main = Project(id = "application, base = file(".")).dependsOn(core)

However, when compiling ApplicationA SBT complains that a dependency can only be a subdirectory!!:

java.lang.AssertionError: assertion failed: Directory C:\git\CoreLibrary is not contained in build root C:\git\ApplicationA

This seems completely straightforward, what's the correct way of having this project dependency?