diff --git a/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/LocalDiskRepositoryTestCase.java b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/LocalDiskRepositoryTestCase.java
index d28c7edb5..568fcdcd0 100644
--- a/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/LocalDiskRepositoryTestCase.java
+++ b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/LocalDiskRepositoryTestCase.java
@@ -114,17 +114,18 @@ public abstract class LocalDiskRepositoryTestCase extends TestCase {
 	protected void setUp() throws Exception {
 		super.setUp();
 
-		if (shutdownHook == null) {
-			shutdownHook = new Thread() {
-				@Override
-				public void run() {
-					System.gc();
-					recursiveDelete("SHUTDOWN", trash, false, false);
-				}
-			};
-			Runtime.getRuntime().addShutdownHook(shutdownHook);
+		synchronized(this) {
+			if (shutdownHook == null) {
+				shutdownHook = new Thread() {
+					@Override
+					public void run() {
+						System.gc();
+						recursiveDelete("SHUTDOWN", trash, false, false);
+					}
+				};
+				Runtime.getRuntime().addShutdownHook(shutdownHook);
+			}
 		}
-
 		recursiveDelete(testName(), trash, true, false);
 
 		mockSystemReader = new MockSystemReader();