diff --git a/make/langtools/src/classes/build/tools/symbolgenerator/CreateSymbols.java b/make/langtools/src/classes/build/tools/symbolgenerator/CreateSymbols.java
index fe5938ce0e3..220face0868 100644
--- a/make/langtools/src/classes/build/tools/symbolgenerator/CreateSymbols.java
+++ b/make/langtools/src/classes/build/tools/symbolgenerator/CreateSymbols.java
@@ -282,6 +282,8 @@ public void createSymbols(String ctDescriptionFileExtra, String ctDescriptionFil
         try (OutputStream fos = new FileOutputStream(ctSymLocation);
              OutputStream bos = new BufferedOutputStream(fos);
              ZipOutputStream jos = new ZipOutputStream(bos)) {
+            // Do not compress ct.sym, allow external compressor to work on it.
+            jos.setLevel(0);
             for (Entry<String, Set<FileData>> e : directory2FileData.entrySet()) {
                 jos.putNextEntry(createZipEntry(e.getKey(), timestamp));
                 for (FileData fd : e.getValue()) {