diff --git a/core/src/main/java/com/threerings/getdown/data/Application.java b/core/src/main/java/com/threerings/getdown/data/Application.java
index 1a4729c..3719d45 100644
--- a/core/src/main/java/com/threerings/getdown/data/Application.java
+++ b/core/src/main/java/com/threerings/getdown/data/Application.java
@@ -431,7 +431,7 @@ public class Application
         try {
             URL remote = new URL(createVAppBase(_targetVersion), encodePath(_javaLocation));
             return new Resource(vmfile, remote, getLocalPath(vmfile),
-                                EnumSet.of(Resource.Attr.UNPACK));
+                                EnumSet.of(Resource.Attr.UNPACK, Resource.Attr.CLEAN));
         } catch (Exception e) {
             log.warning("Failed to create VM resource", "vmfile", vmfile, "appbase", _appbase,
                 "tvers", _targetVersion, "javaloc", _javaLocation, "error", e);
diff --git a/core/src/main/java/com/threerings/getdown/data/Resource.java b/core/src/main/java/com/threerings/getdown/data/Resource.java
index a7601ca..412ce93 100644
--- a/core/src/main/java/com/threerings/getdown/data/Resource.java
+++ b/core/src/main/java/com/threerings/getdown/data/Resource.java
@@ -31,6 +31,9 @@ public class Resource implements Comparable<Resource>
     public static enum Attr {
         /** Indicates that the resource should be unpacked. */
         UNPACK,
+        /** If present, when unpacking a resource, any directories created by the newly
+          * unpacked resource will first be cleared of files before unpacking. */
+        CLEAN,
         /** Indicates that the resource should be marked executable. */
         EXEC
     };
@@ -254,21 +257,20 @@ public class Resource implements Comparable<Resource>
     /**
      * Installs the {@code getLocalNew} version of this resource to {@code getLocal}.
      */
-    public void install (boolean cleanExistingDirs) throws IOException {
+    public void install () throws IOException {
         File source = getLocalNew(), dest = getLocal();
         log.info("- " + source);
         if (!FileUtil.renameTo(source, dest)) {
             throw new IOException("Failed to rename " + source + " to " + dest);
         }
-        applyAttrs(cleanExistingDirs);
+        applyAttrs();
         markAsValid();
     }
 
-
     /**
      * Unpacks this resource file into the directory that contains it.
      */
-    public void unpack (boolean cleanExistingDirs) throws IOException
+    public void unpack () throws IOException
     {
         // sanity check
         if (!_isJar && !_isPacked200Jar) {
@@ -276,35 +278,26 @@ public class Resource implements Comparable<Resource>
         }
         if (_isJar) {
             try (JarFile jar = new JarFile(_local)) {
-                FileUtil.unpackJar(jar, _unpacked, cleanExistingDirs);
+                FileUtil.unpackJar(jar, _unpacked, _attrs.contains(Attr.CLEAN));
             }
         } else {
             FileUtil.unpackPacked200Jar(_local, _unpacked);
         }
     }
-    
-    public void unpack () throws IOException
-    {
-    	unpack(false);
-    }
 
     /**
      * Applies this resources special attributes: unpacks this resource if needed, marks it as
      * executable if needed.
      */
-    public void applyAttrs (boolean cleanExistingDirs) throws IOException {
+    public void applyAttrs () throws IOException {
         if (shouldUnpack()) {
-            unpack(cleanExistingDirs);
+            unpack();
         }
         if (_attrs.contains(Attr.EXEC)) {
             FileUtil.makeExecutable(_local);
         }
     }
 
-    public void applyAttrs () throws IOException {
-    	applyAttrs(false);
-    }
-    
     /**
      * Wipes this resource file along with any "validated" marker file that may be associated with
      * it.
diff --git a/core/src/main/java/com/threerings/getdown/util/FileUtil.java b/core/src/main/java/com/threerings/getdown/util/FileUtil.java
index 0008a4f..378f701 100644
--- a/core/src/main/java/com/threerings/getdown/util/FileUtil.java
+++ b/core/src/main/java/com/threerings/getdown/util/FileUtil.java
@@ -93,26 +93,29 @@ public class FileUtil
 
     /**
      * Unpacks the specified jar file into the specified target directory.
+     * @param cleanExistingDirs if true, all files in all directories contained in {@code jar} will
+     * be deleted prior to unpacking the jar.
      */
-    public static void unpackJar (JarFile jar, File target, boolean cleanExistingDirs) throws IOException
+    public static void unpackJar (JarFile jar, File target, boolean cleanExistingDirs)
+        throws IOException
     {
-        Enumeration<?> entries = jar.entries();
-        if (cleanExistingDirs)
-        {
-			while (entries.hasMoreElements()) {
-				JarEntry entry = (JarEntry) entries.nextElement();
-				if (entry.isDirectory()) {
-					File efile = new File(target, entry.getName());
-					 if (efile.exists()) {
-						 for (File f : efile.listFiles()) {
-							 if (!f.isDirectory())
-								 f.delete();
-						 }
-					 }
-				}
-			}
+        if (cleanExistingDirs) {
+            Enumeration<?> entries = jar.entries();
+            while (entries.hasMoreElements()) {
+                JarEntry entry = (JarEntry)entries.nextElement();
+                if (entry.isDirectory()) {
+                    File efile = new File(target, entry.getName());
+                    if (efile.exists()) {
+                        for (File f : efile.listFiles()) {
+                            if (!f.isDirectory())
+                            f.delete();
+                        }
+                    }
+                }
+            }
         }
-        entries = jar.entries();
+
+        Enumeration<?> entries = jar.entries();
         while (entries.hasMoreElements()) {
             JarEntry entry = (JarEntry)entries.nextElement();
             File efile = new File(target, entry.getName());
diff --git a/launcher/src/main/java/com/threerings/getdown/launcher/Getdown.java b/launcher/src/main/java/com/threerings/getdown/launcher/Getdown.java
index a970c01..17368b1 100644
--- a/launcher/src/main/java/com/threerings/getdown/launcher/Getdown.java
+++ b/launcher/src/main/java/com/threerings/getdown/launcher/Getdown.java
@@ -116,7 +116,7 @@ public abstract class Getdown extends Thread
         } else if (_readyToInstall) {
             log.info("Installing " + _toInstallResources.size() + " downloaded resources:");
             for (Resource resource : _toInstallResources) {
-                resource.install(false);
+                resource.install();
             }
             _toInstallResources.clear();
             _readyToInstall = false;
@@ -589,7 +589,7 @@ public abstract class Getdown extends Thread
         reportTrackingEvent("jvm_unpack", -1);
 
         updateStatus("m.unpacking_java");
-        vmjar.install(true);
+        vmjar.install();
 
         // these only run on non-Windows platforms, so we use Unix file separators
         String localJavaDir = LaunchUtil.LOCAL_JAVA_DIR + "/";