diff --git a/dev/core/src/com/google/gwt/dev/javac/UnitCacheFactory.java b/dev/core/src/com/google/gwt/dev/javac/UnitCacheFactory.java
index 8083790..1708de3 100644
--- a/dev/core/src/com/google/gwt/dev/javac/UnitCacheFactory.java
+++ b/dev/core/src/com/google/gwt/dev/javac/UnitCacheFactory.java
@@ -28,8 +28,10 @@
   /**
    * The API must be enabled explicitly for persistent caching to be live.
    */
-  private static final boolean usePersistent = System.getProperties().containsKey(
-      "gwt.persistentunitcache");
+  private static final String configPropertyValue = System.getProperty("gwt.persistentunitcache",
+      "false");
+  private static final boolean usePersistent = configPropertyValue.length() == 0
+      || Boolean.parseBoolean(configPropertyValue);
   private static UnitCache instance = null;
 
   /**