--- a/langtools/src/jdk.jshell/share/classes/jdk/jshell/JShell.java	Tue Aug 15 13:16:32 2017 -0700
+++ b/langtools/src/jdk.jshell/share/classes/jdk/jshell/JShell.java	Wed Aug 16 18:42:11 2017 -0700
@@ -862,7 +862,7 @@
      * Check if this JShell has been closed
      * @throws IllegalStateException if it is closed
      */
-    private void checkIfAlive()  throws IllegalStateException {
+    void checkIfAlive()  throws IllegalStateException {
         if (closed) {
             throw new IllegalStateException(messageFormat("jshell.exc.closed", this));
         }
@@ -879,8 +879,8 @@
         if (sn == null) {
             throw new NullPointerException(messageFormat("jshell.exc.null"));
         } else {
-            if (sn.key().state() != this) {
-                throw new IllegalArgumentException(messageFormat("jshell.exc.alien"));
+            if (sn.key().state() != this || sn.id() == Snippet.UNASSOCIATED_ID) {
+                throw new IllegalArgumentException(messageFormat("jshell.exc.alien", sn.toString()));
             }
             return sn;
         }