diff --git a/src/share/classes/java/util/zip/Deflater.java b/src/share/classes/java/util/zip/Deflater.java
index c4521bec667bee513c5bc8850e8f030c226c98b4..3bb5f9901ba61524e6c73123849f5193aaf0c765 100644
--- a/src/share/classes/java/util/zip/Deflater.java
+++ b/src/share/classes/java/util/zip/Deflater.java
@@ -318,7 +318,9 @@ class Deflater {
      * should be called in order to provide more input
      */
     public boolean needsInput() {
-        return len <= 0;
+        synchronized (zsRef) {
+            return len <= 0;
+        }
     }
 
     /**