diff --git a/src/java/org/apache/lucene/store/RAMDirectory.java b/src/java/org/apache/lucene/store/RAMDirectory.java
index a1dcb67fd38..c68e767945e 100644
--- a/src/java/org/apache/lucene/store/RAMDirectory.java
+++ b/src/java/org/apache/lucene/store/RAMDirectory.java
@@ -180,7 +180,7 @@ public class RAMDirectory extends Directory implements Serializable {
     synchronized (this) {
       RAMFile existing = fileMap.get(name);
       if (existing!=null) {
-        sizeInBytes.addAndGet(existing.sizeInBytes);
+        sizeInBytes.addAndGet(-existing.sizeInBytes);
         existing.directory = null;
       }
       fileMap.put(name, file);