diff --git a/project/SparkBuild.scala b/project/SparkBuild.scala
index 7c004df6fb8b23a30ce4fcff5d5a37cee6ed27f3..7bd6c4c2355f37cd05fd117bcb8220ef2779507e 100644
--- a/project/SparkBuild.scala
+++ b/project/SparkBuild.scala
@@ -56,6 +56,9 @@ object SparkBuild extends Build {
     fork := true,
     javaOptions += "-Xmx2g",
 
+    // Only allow one test at a time, even across projects, since they run in the same JVM
+    concurrentRestrictions in Global += Tags.limit(Tags.Test, 1),
+
     // Shared between both core and streaming.
     resolvers ++= Seq("Akka Repository" at "http://repo.akka.io/releases/"),