diff --git a/build.gradle b/build.gradle
index fde0be6c..57287a7a 100644
--- a/build.gradle
+++ b/build.gradle
@@ -35,7 +35,8 @@ subprojects {
   apply plugin: 'eclipse'
   apply plugin: 'java'
 
-  sourceCompatibility = 1.7
+  sourceCompatibility = 1.6
+  targetCompatibility = 1.6
 
   tasks.withType(JavaCompile) {
       options.encoding = 'UTF-8'
diff --git a/xtext-gradle-builder/src/main/java/org/xtext/gradle/builder/XtextGradleBuilder.xtend b/xtext-gradle-builder/src/main/java/org/xtext/gradle/builder/XtextGradleBuilder.xtend
index 5937628c..8f201a27 100644
--- a/xtext-gradle-builder/src/main/java/org/xtext/gradle/builder/XtextGradleBuilder.xtend
+++ b/xtext-gradle-builder/src/main/java/org/xtext/gradle/builder/XtextGradleBuilder.xtend
@@ -37,6 +37,7 @@ import org.xtext.gradle.protocol.GradleInstallDebugInfoRequest
 import org.xtext.gradle.protocol.IncrementalXtextBuilder
 
 import static org.eclipse.xtext.util.UriUtil.createFolderURI
+import java.io.Closeable
 
 class XtextGradleBuilder implements IncrementalXtextBuilder {
 	val index = new GradleResourceDescriptions
@@ -174,10 +175,12 @@ class XtextGradleBuilder implements IncrementalXtextBuilder {
 	private def cleanup(GradleBuildRequest gradleRequest, BuildRequest request) {
 		val resourceSet = request.resourceSet
 		val jvmTypesLoader = resourceSet.classpathURIContext as URLClassLoader
-		try {
-			jvmTypesLoader.close
-		} catch (Exception e) {
-			gradleRequest.logger.debug("Couldn't close jvm types classloader", e)
+		if (jvmTypesLoader instanceof Closeable) { // URLClassLoader has no close method in Java 6
+			try {
+				jvmTypesLoader.close
+			} catch (Exception e) {
+				gradleRequest.logger.debug("Couldn't close jvm types classloader", e)
+			}
 		}
 		resourceSet.resources.clear
 		resourceSet.eAdapters.clear