diff --git a/src/share/classes/java/lang/ProcessBuilder.java b/src/share/classes/java/lang/ProcessBuilder.java
index be24e8d8235414a8080d275810425e7f18fa767e..228c75d8cc5db632a39a10abc98fc9bf8d7d8bdd 100644
--- a/src/share/classes/java/lang/ProcessBuilder.java
+++ b/src/share/classes/java/lang/ProcessBuilder.java
@@ -994,6 +994,8 @@ public final class ProcessBuilder
         // Must convert to array first -- a malicious user-supplied
         // list might try to circumvent the security check.
         String[] cmdarray = command.toArray(new String[command.size()]);
+        cmdarray = cmdarray.clone();
+
         for (String arg : cmdarray)
             if (arg == null)
                 throw new NullPointerException();