diff --git a/sbt/src/sbt-test/tests/fork-parallel/project/ForkParallelTest.scala b/sbt/src/sbt-test/tests/fork-parallel/project/ForkParallelTest.scala
index c54748b65..891658ddf 100644
--- a/sbt/src/sbt-test/tests/fork-parallel/project/ForkParallelTest.scala
+++ b/sbt/src/sbt-test/tests/fork-parallel/project/ForkParallelTest.scala
@@ -11,8 +11,16 @@ object ForkParallelTest extends Build {
 		libraryDependencies += "com.novocode" % "junit-interface" % "0.10" % "test",
 		fork in Test := true,
 		check := {
-			if( ! (file("max-concurrent-tests_3").exists() || file("max-concurrent-tests_4").exists() )) {
-				sys.error("Forked tests were not executed in parallel!")
+			val nbProc = java.lang.Runtime.getRuntime().availableProcessors()
+			if( nbProc < 4 ) {
+				streams.value.log.warn("With fewer than 4 processors this test is meaningless")
+			} else {
+				// we've got at least 4 processors, we'll check the upper end but also 3 and 4 as the upper might not
+				// be reached if the system is under heavy load.
+				if( ! (file("max-concurrent-tests_3").exists() || file("max-concurrent-tests_4").exists() ||
+							 file("max-concurrent-tests_" + (nbProc -1)).exists() || file("max-concurrent-tests_" + nbProc).exists())) {
+					sys.error("Forked tests were not executed in parallel!")
+				}
 			}
 		}
 	))