--- a/langtools/src/share/classes/com/sun/tools/javac/code/Types.java	Thu Jan 29 12:18:19 2009 +0000
+++ b/langtools/src/share/classes/com/sun/tools/javac/code/Types.java	Thu Jan 29 12:19:14 2009 +0000
@@ -2131,9 +2131,6 @@
                                   List<Type> to) {
         if (tvars.isEmpty())
             return tvars;
-        if (tvars.tail.isEmpty())
-            // fast common case
-            return List.<Type>of(substBound((TypeVar)tvars.head, from, to));
         ListBuffer<Type> newBoundsBuf = lb();
         boolean changed = false;
         // calculate new bounds
@@ -2173,8 +2170,14 @@
         Type bound1 = subst(t.bound, from, to);
         if (bound1 == t.bound)
             return t;
-        else
-            return new TypeVar(t.tsym, bound1, syms.botType);
+        else {
+            // create new type variable without bounds
+            TypeVar tv = new TypeVar(t.tsym, null, syms.botType);
+            // the new bound should use the new type variable in place
+            // of the old
+            tv.bound = subst(bound1, List.<Type>of(t), List.<Type>of(tv));
+            return tv;
+        }
     }
     // </editor-fold>
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/test/tools/javac/generics/6729401/T6729401.java	Thu Jan 29 12:19:14 2009 +0000
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2008 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * @test
+ * @bug 6729401
+ *
+ * @summary  Compiler error when using F-bounded generics with free type variables
+ * @author Maurizio Cimadamore
+ * @compile T6729401.java
+ *
+ */
+
+class T6729401 {
+
+    interface I<U,W> {
+        <T extends I<U,T>> void m(I<U,T> x);
+    }
+
+    <X extends I<Object,X>,Y extends I<Object,Y>> void test(I<Object,X> x, I<Object,Y> y) {
+        x.<Y>m(y);
+        x.m(y);
+        y.<X>m(x);
+        y.m(x);
+    }
+}