diff --git a/src/sphinx/Detailed-Topics/Testing.rst b/src/sphinx/Detailed-Topics/Testing.rst
index 120c1b740..c3ff52fa3 100644
--- a/src/sphinx/Detailed-Topics/Testing.rst
+++ b/src/sphinx/Detailed-Topics/Testing.rst
@@ -191,7 +191,7 @@ The setting:
 specifies that all tests will be executed in a single external JVM. See
 :doc:`Forking` for configuring standard options for forking. More control
 over how tests are assigned to JVMs and what options to pass to those is
-available with :key:`testGrouping` key. For example:
+available with :key:`testGrouping` key. For example in build.sbt:
 
 ::
 
@@ -201,8 +201,9 @@ available with :key:`testGrouping` key. For example:
       def groupByFirst(tests: Seq[TestDefinition]) =
         tests groupBy (_.name(0)) map {
           case (letter, tests) => new Group(letter.toString, tests, SubProcess(Seq("-Dfirst.letter"+letter)))
-        } toSeq;
-      testGrouping := groupByFirst( (definedTests in Test).value )
+        } toSeq
+
+        testGrouping in Test <<= groupByFirst( (definedTests in Test).value )
     }
 
 The tests in a single group are run sequentially. Control the number