diff --git a/build.sbt b/build.sbt
index ae26c3b..ebaa46e 100644
--- a/build.sbt
+++ b/build.sbt
@@ -6,7 +6,9 @@ organization := "com.samskivert"
 
 crossPaths := false
 
-javacOptions ++= Seq("-Xlint", "-Xlint:-serial")
+javacOptions ++= Seq(
+  "-Xlint", "-Xlint:-serial", "-source", "1.6", "-target", "1.6"
+)
 
 autoScalaLibrary := false // no scala-library dependency